                            In the

United States Court of Appeals
              For the Seventh Circuit

No. 07-1134

U NITED S TATES OF A MERICA,
                                                Plaintiff-Appellee,
                                v.

JAVIER H ERNANDEZ,
                                            Defendant-Appellant.


           Appeal from the United States District Court
                for the Central District of Illinois.
           No. 05 CR 10062—Joe Billy McDade, Judge.



   A RGUED JANUARY 14, 2008—D ECIDED S EPTEMBER 12, 2008




 Before P OSNER, K ANNE, and W ILLIAMS, Circuit Judges.
  W ILLIAMS, Circuit Judge. Javier Hernandez pled guilty
to conspiring to knowingly distribute cocaine. In the
plea agreement, the parties agreed to have the district
court determine, beyond a reasonable doubt, the quantity
of drugs for which Hernandez would be held accountable
in determining his sentence. Because it is unclear how the
district court arrived at its drug quantity calculation,
we cannot determine whether the government met its
2                                             No. 07-1134

burden so we find that the district court committed clear
error. We remand this case to the district court to deter-
mine the amount of drugs attributable to Hernandez.


                  I. BACKGROUND
  Javier Hernandez was charged with conspiring to
knowingly distribute cocaine, in violation of 21 U.S.C.
§ 841(a)(1). The indictment alleged that more than five
kilograms of cocaine and fifty grams of crack were in-
volved in the conspiracy. Pursuant to his plea agreement,
Hernandez pled guilty to distributing only one kilogram
of cocaine. His plea agreement also stipulated that any
further drug quantities had to be proven beyond a rea-
sonable doubt at sentencing. The district court agreed to
apply the burden of proof stipulated to by the parties in
determining the drug quantity attributable to Hernandez.
At the sentencing hearing, Darrell Daily, Melvin Harmon,
Troy Powers, and Eric Keith testified that Hernandez
provided them with at least 196 kilograms of cocaine
over the course of the conspiracy. Daily testified that in
September of 2001, Hernandez supplied him with one
kilogram of cocaine. Daily then sold this cocaine to
Harmon, who sold it to Dumond and Courtney Morris.
Hernandez later provided Daily with another kilogram
of cocaine after Harmon indicated that the first kilogram
was “bad,” or unusable. In the remaining months of 2001,
Daily continued to sell small amounts of cocaine to the
Morrises indirectly through Harmon. Harmon testified
that he sold two to three kilograms per month to the
Morrises for the remaining months of 2001.
No. 07-1134                                             3

  According to the testimony at the hearing, the drug
quantities that Daily obtained from Hernandez increased
substantially in 2002. In 2002, Hernandez supplied Daily
with between one and twelve kilograms of cocaine on
multiple occasions, and seventeen kilograms of cocaine
on one occasion. Daily supplied Harmon, who sold the
Morrises at least six kilograms of cocaine every month in
2002. There were also at least two occasions in 2002 where
Daily supplied the Morrises directly with six to seven
kilograms of cocaine. By this time, Daily had a supplier
other than Hernandez, but it is not clear if Daily began
purchasing cocaine from this alternate source in 2002
or 2003.
  In 2003, Daily sold approximately twenty-five kilograms
of cocaine to Harmon. In late 2003, Hernandez provided
Harmon with fifty kilograms of cocaine directly. In
2004, Hernandez continued to supply Harmon, who sold
approximately seventy kilograms of cocaine to the
Morrises that year. Harmon was arrested in March 2005
for attempting to sell one kilogram of cocaine, which
had been provided by Hernandez, to a third party.
  Powers testified that in the fall of 2003, he purchased
four and a half ounces of cocaine from Hernandez. He
also purchased a similar amount of cocaine from
Hernandez on two to three other occasions that year. In
2004 and 2005, Powers purchased one to three kilograms
of cocaine once or twice a month from Hernandez until
Hernandez’s arrest in June 2005. Powers estimated that he
received fifteen to twenty kilograms of cocaine from
Hernandez from early 2004 until June 2005.
4                                               No. 07-1134

  Harmon introduced Keith into the drug scheme, and
both Harmon and Daily supplied Keith. Keith testified
that from 2001 until 2004, he obtained at least one kilo-
gram of cocaine a week from Harmon until Keith’s arrest
in 2004. In 2002, Daily sold Keith six to seven grams of
cocaine, which were provided by Harmon. Keith testified
that, by the time of his arrest, he had received seventy
kilograms of cocaine from Harmon and five from Daily.
All of the cocaine involved in these transactions originated
from Hernandez. In 2004, Keith obtained five kilograms of
cocaine directly from Hernandez.
  Hernandez did not present any witnesses at the hearing,
but during cross-examination of the government’s wit-
nesses, his attorney elicited testimony indicating that they
had made prior inconsistent statements to the agents
investigating the case. Hernandez argued that the wit-
nesses were biased because they were receiving benefits
from the government in exchange for their testimony, and
there were no drug ledgers or other records to corroborate
their testimony. In response, the government contended
that the witnesses established that Hernandez was respon-
sible for distributing at least 196 kilograms of powder
cocaine—eight kilograms in 2001; seventy-two kilograms
in 2002; twenty-five kilograms in 2003; seventy-five
kilograms in 2004; and sixteen kilograms in 2005. The
district court ultimately concluded that Hernandez was
responsible for distributing 159 kilograms of cocaine,
which it considered a “conservative” estimate based on its
consideration of the credibility of the witnesses. The court
did not explain how it arrived at 159 kilograms, but did
indicate that its decision was made beyond a reason-
able doubt.
No. 07-1134                                                5

  The finding of 159 kilograms resulted in Hernandez
having a base offense level of 38. After applying a four-
level enhancement for his leadership role in the offense
and awarding a two-level reduction for acceptance of
responsibility, the court determined that Hernandez had
an offense level of 40. With a Criminal History Category of
IV, the resulting advisory guidelines range was 360 months
to life. The court sentenced Hernandez to 360 months
in prison. Hernandez appeals, arguing that there was
insufficient evidence to support the district court’s sen-
tencing determination regarding drug quantity.


                      II. ANALYSIS
  A. The district court did not commit clear error by
     crediting the testimony of the government’s wit-
     nesses at the sentencing hearing.
  We review the district court’s application of the sentenc-
ing guidelines de novo and its factual findings under the
clearly erroneous standard of review. United States v.
Bennett, 461 F.3d 910, 912 (7th Cir. 2006). We will reverse
the district court’s factual findings only where there is a
“definite and firm conviction that a mistake has been
committed.” Id.; United States v. Noble, 246 F.3d 946, 951
(7th Cir. 2001). In determining a drug offender’s base
offense level, a district court considers quantities of drugs
specified in the count of conviction and the quantities
that were part of the same course of conduct or common
scheme or plan as the offense of conviction. See U.S.S.G.
§ 1B1.3(a)(2); United States v. Huerta, 239 F.3d 865, 875
(7th Cir. 2001). In doing so, “the district court is entitled
6                                               No. 07-1134

to estimate drug quantity using testimony about the
frequency of dealing and the amount dealt over a specified
period of time.” Noble, 246 F.3d at 952 (internal citations
omitted).
   Hernandez disputes the drug quantity determination
made by the district court, arguing that the witnesses
who testified against him were not credible, and that the
government failed to present any evidence to corroborate
their testimony, such as ledgers or records memorializing
the drug transactions. We have held, however, that
“uncorroborated evidence can be a sufficient basis for a
sentence.” United States v. Johnson, 227 F.3d 807, 813 (7th
Cir. 2000). Hernandez’s arguments regarding witness
credibility are also not persuasive. We are “reluctant to
disturb credibility determinations absent a compelling
reason,” Noble, 246 F.3d at 951, and here, no compelling
reason exists. Hernandez focuses most of his efforts on
undermining the credibility of Daily and Keith, whose
testimony contained gaps and inconsistencies. Hernandez
argues that Keith is unreliable because Keith testified that
he named Hernandez as his supplier to the agents who
arrested Keith, but Hernandez is never mentioned in
the agents’ reports. Keith eventually told the agents that
he had purchased cocaine directly from Hernandez, but
it was two years after his initial arrest. This two year gap,
Hernandez maintains, destroys Keith’s credibility.
  The omission of Hernandez from the agents’ reports,
however, does not necessarily conflict with Keith’s later
testimony that Hernandez was his supplier. Keith indi-
cated on cross-examination that he did not mention
No. 07-1134                                              7

Hernandez because he was not asked about any of his
transactions or dealings with Hernandez; additionally, he
testified that he had discussed Hernandez on occasions
that were not mentioned in the reports. Although Keith
does not identify Hernandez as his supplier until two years
after his arrest, Keith first mentioned Hernandez to the
agents three weeks after Keith’s arrest. Keith mentioned to
the agents that at one of his transactions with Harmon, he
saw someone that he believed to be Harmon’s supplier,
whom he referred to as “Javy,” which is Hernandez’s
nickname. During this incident, Hernandez brought the
cocaine to Harmon, who then sold it to Keith. From this
perspective, the district court could have concluded that,
despite the time gap, Keith’s testimony that he bought
five kilograms directly from Hernandez is credible
because Keith identified Hernandez as the supplier of
the cocaine that he had purchased during his early trans-
actions with Harmon. It would not be a stretch to believe
that Keith later obtained cocaine from Hernandez directly.
  Hernandez also tried to discredit Harmon’s testimony
that he received approximately seventy-two kilograms of
cocaine indirectly through Hernandez in 2002 because
Harmon testified that he never went with Daily to meet
Hernandez to pick up the drugs. The fact that Harmon
never went with Daily to get drugs from Hernandez does
not mean that Hernandez did not supply Daily with the
drugs that Harmon received. Harmon testified that
“I would inform Darrell Daily that I needed a certain
amount of—certain amount of kilos . . . and then I would
meet up with him at his house and I would wait and then
Javier would come in and then would leave, then I would
8                                                   No. 07-1134

have the amount that I was waiting for.” From this testi-
mony, there is a strong inference that Hernandez was the
source of the drugs that Daily provided to Harmon. In
fact, Daily testified that in 2002 he received between one
and twelve kilograms of cocaine from Hernandez on
multiple occasions and seventeen kilograms on one
occasion in particular, and Daily was Harmon’s supplier.
  Nonetheless, as Hernandez points out, there were
inconsistencies in the testimony of the witnesses, particu-
larly Daily. Discrepancies or inconsistent prior state-
ments do not, as a matter of law, render a witness’s
testimony incredible. United States v. Alcantar, 83 F.3d 185,
189-90 (7th Cir. 1996). “In order for testimony to be found
incredible as a matter of law, ‘it must have been either
physically impossible for the witness to observe that
which he or she claims occurred, or impossible under
the laws of nature for the occurrence to have taken place
at all.’ ” United States v. Ortiz, 431 F.3d 1035, 1039 (7th Ci r.
2005) (citing United States v. McEntire, 153 F.3d 424, 435 (7th
Cir. 1998)).
  Here the testimony was neither impossible nor improba-
ble, and in fact, the prosecutor tried to account for incon-
sistencies in the witnesses’ testimony by excluding cer-
tain amounts where appropriate. For example, Daily gave
conflicting testimony about when he started receiving
cocaine from a source other than Hernandez, so the
government did not rely on Daily’s testimony in calculat-
ing Hernandez’s drug quantity for the year 2003. Addition-
ally, Daily testified that ninety percent of his supply
came from Hernandez in 2002, leading the prosecutor to
No. 07-1134                                               9

proportionately discount the amount attributed to
Hernandez for that year. Also, Harmon initially told
authorities that he bought approximately twenty-five
kilograms of cocaine directly from Hernandez in 2004,
but later testified that he obtained fifty to seventy-five
kilograms of cocaine. The prosecutor asked the court to
hold Hernandez responsible for only twenty-five kilograms
of cocaine, rather than fifty or seventy-five kilograms.
  Furthermore, the witnesses’ testimonies were fairly con-
sistent with regards to the hierarchy of the drug operation;
the business arrangement with the Morrises; and Keith’s
introduction into the drug scheme. Daily and Harmon
corroborated each other’s testimony in describing the
formation of the drug operation in prison and their
initial transaction with the Morrises. They also testified
similarly as to the later transactions with the Morrises as
well as the introduction of Keith, another of Harmon’s
former prison mates, into the drug scheme. There was
also overlap in testimony regarding the drug quanti-
ties—for example, Daily testified that in 2001 and 2002,
ninety percent of his supply of cocaine came from
Hernandez, which was approximately eighty kilograms.
Harmon’s testimony regarding his distributions to the
Morrises was that during those years he sold them approx-
imately eighty kilograms of cocaine, all of which were
supplied by Daily. Thus, there is some indicia of reli-
ability to the witnesses’ testimony which, when combined
with their testimony about the frequency and amount of
the drug dealing, could have reasonably led the district
court to conclude that much of their testimony was credi-
ble. Noble, 246 F.3d at 952 (“The district court is entitled
to estimate drug quantity using testimony about the
10                                             No. 07-1134

frequency of dealing and the amount dealt over a specified
period of time”) (citing United States v. Durham, 211 F.3d
437, 444 (7th Cir. 2000)).
   Finally, Hernandez argues that because Daily, Harmon,
and Powers are convicted felons, this fact in and of itself
impeaches their credibility. This argument need not
detain us long. While this is one factor that the district
court can consider in weighing the evidence, it is also
within the district court’s discretion to give some weight
to their testimony, notwithstanding their status as felons.
United States v. Johnson, 489 F.3d 794, 797 (7th Cir. 2007)
(noting that the district court can credit testimony that
is “totally uncorroborated and comes from an admitted
liar, convicted felon, large scale drug-dealing, paid gov-
ernment informant”). Accordingly, we find that the
district court did not commit clear error in finding that
the government’s witnesses were credible.


 B. The district court’s drug quantity calculation was
    clearly erroneous because the district court failed to
    specify how it determined the amount of drugs
    attributable to Hernandez.
   While the district court could conclude, based on the
testimony at the sentencing hearing, that Hernandez
conspired to distribute more than 150 kilograms of cocaine,
it is unclear how it arrived at the 159 kilograms that it
ultimately settled on as the drug quantity amount. The
government agrees that, based on the testimony at the
sentencing hearing, there is no way to arrive at 159 kilo-
grams as the amount of cocaine attributable to Hernandez.
No. 07-1134                                               11

From the record, it is apparent that the district court
weighed any perceived conflicts in the testimony, the
witnesses’ felon status, and the imprecise nature of the
drug calculations in reducing Hernandez’s drug quantity
amount by almost forty kilograms from what the govern-
ment asked it to consider in imposing sentence. Further,
the district court indicated that its estimate was “conserva-
tive,” suggesting that it believed that Hernandez was
responsible for more drugs than it actually attributed
to him.
   The district court’s failure to indicate how it arrived at
its drug quantity calculation is problematic, however,
because Hernandez’s base offense level of 40 corresponds
to a drug quantity amount of 150 kilograms or more of
cocaine; the court settled on 159 kilograms, which is
extremely close to the cutoff of 150 kilograms. See U.S.S.G.
§ 2D1.1. Had it reduced the drug quantity finding by an
additional nine kilograms, the base offense level would
have been 36 (the range for 50 to 150 kilograms of cocaine)
which, with the four-level enhancement for leadership
role in an offense and two-level reduction for acceptance
of responsibility, would have been a base offense level of
38. Given Hernandez’s Criminal History Category of IV,
the advisory guidelines range would be 262-327 months,
rather than the range of 360 months to life used by the
district court. See U.S.S.G. § 5A.
  It is clear that in Hernandez’s situation, where the
district court’s drug quantity calculation placed him on
the cusp of a lower guidelines range, every kilogram
counts. In particular, Daily’s testimony leaves the most
12                                                No. 07-1134

room for error. While the government discounted much of
Daily’s testimony in calculating its drug quantity recom-
mendation, it is not clear what portions of Daily’s testi-
mony the district court credited in determining the drug
quantity amount attributable to Hernandez. Daily testified
that he started buying cocaine from a supplier other
than Hernandez in 2002 because of the incident with
the “bad kilo,” but Daily’s proffer statement, which
was used to refresh his recollection at the sentencing,
indicated that Daily first started buying cocaine from
the alternate source in May of 2003. While the govern-
ment did not include any of Hernandez’s sales to Daily
in 2003 in its drug quantity calculation because of this
discrepancy, it is not clear if the district court also reduced
the drug quantity amount for 2002 based on Daily’s
conflicting testimony that he purchased drugs from an
individual other than Hernandez that year.
  In addition, Daily initially testified that approximately
ninety percent of the cocaine that he sold to the Morrises
from 2001 until 2003, either directly or through Harmon,
was provided by Hernandez, but later changed his testi-
mony to suggest that the ninety percent figure might not
be entirely correct and that Hernandez might not have
been Daily’s primary source. This testimony suggests that
Hernandez’s drug sales to Daily may have been less than
the amount of drugs that the government sought to
attribute to Hernandez from 2001 until 2003.
 In contrast, Harmon’s testimony indicates that
Hernandez might be responsible for more than the drug
quantity that the government attributed to Hernandez
No. 07-1134                                                 13

for the year 2002. For example, Harmon testified that
there was at least one instance in 2002 were he provided
eight kilograms of cocaine to the Morrises. In calculating
drug quantity for 2002, the prosecutor did not include
this figure, opting instead to rely on Harmon’s testimony
that he provided at least six kilograms to the Morrises
every month in 2002. The prosecutor also relied on the
lower estimate regarding the drugs that Hernandez sold
to Harmon in 2004, relying on the figure of twenty-five
kilograms because of discrepancies in Harmon’s testimony,
even though Harmon testified that he was obtaining, on
average, ten kilograms a month from Hernandez during
that year, and at one point, had obtained eighteen kilo-
grams of cocaine from Hernandez to sell to the Morrises.
While the prosecutor’s reliance on the lower drug
amount is certainly not problematic, these discrepancies
illustrate the need for specificity by the district court as to
what testimony it relied on in calculating the 159 kilograms
it ultimately held Hernandez responsible for, especially
given this amount’s proximity to the cutoff for the
lower base offense level, which corresponds to a drug
quantity amount of 50-150 kilograms of cocaine.
  We have long recognized that the drug quantity calcula-
tion is necessarily imprecise because “drug dealers ordi-
narily do not use invoices and bills of lading”; therefore,
“sentencing courts may make reasonable estimates as to
drug quantities.” United States v. Rodriguez, 67 F.3d 1312,
1325 (7th Cir. 1995). Here, the district court’s determina-
tion that Hernandez was responsible for 159 kilograms
might be a “conservative” estimate given that the gov-
ernment asked it to attribute a drug quantity of 196
14                                                 No. 07-1134

kilograms to Hernandez. We also know that the district
court did not count eighteen kilograms of cocaine that
Hernandez supplied to Powers through a third party after
his arrest. Although the district court reduced the drug
quantity calculation recommended by the government
by almost forty kilograms because of the various con-
tradictions and inconsistencies present in the witnesses’
testimony, the district court does not indicate which
amounts it actually relied on in calculating the 159 kilo-
grams that it ultimately attributed to Hernandez. Given
the various amounts mentioned during the testimony at
sentencing and the fact that the district court did not
explain how it determined its drug quantity calculation,
it is impossible for us to find that there was no error in
the calculation.


    C. The parties can stipulate to a different burden of
       proof than that required by law, but we cannot
       determine from the record if the government met
       its burden.
  In the plea agreement, the parties stipulated that the
government has the burden of proving the quantity of
drugs attributable to Hernandez beyond a reasonable
doubt at sentencing.1 Usually, the district court makes


1
  The defendant also argues that the district court should have
adhered to the Federal Rules of Evidence at his sentencing
hearing because the parties agreed to a higher burden of proof.
The defendant offers no authority for this position and the
                                                  (continued...)
No. 07-1134                                                 15

drug quantity findings at sentencing based on the prepon-
derance standard. United States v. Spiller, 261 F.3d 683, 691
(7th Cir. 2001) (“[A]t sentencing, the Government must
prove the facts underlying the base offense or an enhance-
ment by a preponderance of the evidence.”) (internal
citation and quotation omitted). Nevertheless, the district
court stated that it made its findings consistent with the
standard agreed on by the parties because it assumed it
was bound by the stipulation. As a general matter, we do
not subscribe to the idea that the court was bound by the
parties’ stipulation. United States v. Mankiewicz, 122 F.3d
399, 403 n.1 (7th Cir. 1997) (“As the Guidelines themselves
make clear, although the plea agreement binds the parties,
it does not bind the court.”); see also U.S.S.G. § 6B1.4(d)
(stating that parties can stipulate to facts relevant to
sentencing as a part of a plea agreement, but the court is
not obligated to accept the stipulation).
   In fact, a district court can reject a plea agreement in
its entirety as long as the court “articulates a sound reason
for rejecting the agreement.” United States v. King, 506 F.3d
532, 535 (7th Cir. 2007) (affirming the district court’s
rejection of a plea agreement on the basis that the sen-
tence within the parties’ proposed guidelines range
would have been too low to achieve the sentencing goals
enumerated in 18 U.S.C. § 3553(a)); see also Fed. R. Crim. P.
11(c)(5) (discussing circumstances in which a district



1
  (...continued)
parties did not explicitly agree to such an arrangement. There-
fore, we will not read new terms into the plea agreement.
16                                                 No. 07-1134

court can reject a plea agreement). This is particularly
true here where the parties have stipulated, not to specific
facts, but to a different standard for the applicable burden
of proof at sentencing. See Swift & Co. v. Hocking Valley R.
Co., 243 U.S. 281, 290 (1917) (“the court cannot be con-
trolled by agreement of counsel on a subsidiary question
of law”); United States v. One 1978 Bell Jet Ranger Helicopter,
707 F.2d 461, 462 (11th Cir. 1983) (“a stipulation of the
parties to an action may be ignored by the court if it is a
stipulation as to what the law requires”); King v. United
States, 641 F.2d 253, 258 (5th Cir. 1981) (same).
  However, where a court opts to enforce a plea agree-
ment, it should adhere to the terms agreed upon by the
parties. Plea agreements are contracts, and should be
interpreted according to principles of contract law. United
States v. Randle, 324 F.3d 550, 557-58 (7th Cir. 2003) (citing
United States v. Williams, 102 F.3d 923, 926-27 (7th Cir.
1996)). Like other contracts, plea agreements should be
enforced consistent with the intent of the parties and the
language of the agreement. United States v. Atkinson, 259
F.3d 648, 654 (7th Cir. 2001) (“[W]e review the language
of the plea agreement objectively and hold the govern-
ment to the literal terms of the plea agreement.”) (citation
omitted).
  The district court opted to enforce the stipulation.
Initially, we note that there does not appear to be any harm
from its decision to do so.2 Unlike a situation in which a


2
   Although neither side challenges the validity of the stipula-
tion, where the parties have changed the burden of proof
                                                  (continued...)
No. 07-1134                                                   17

defendant has waived one of his rights as a part of a
constitutionally impermissible plea agreement, or where
the parties have stipulated to some unorthodox practice,
the same concerns are not present here. See United States v.
Hicks, 129 F.3d 376, 377 (7th Cir. 1997) (“a sentence based
on constitutionally impermissible criteria, such as race,
is invalid even though the defendant executed a blanket
waiver of his rights”); United States v. Feichtinger, 105 F.3d
1188, 1190 (7th Cir. 1997) (a sentence in excess of the
statutory maximum sentence for the defendant’s crime
invalidates sentence, notwithstanding defendant’s stipula-
tion waiving his right to appeal); United States v. Andrews,
895 F.2d 406, 409 (7th Cir. 1990) (where the defendant
waived his right to have a trial declared a mistrial after
extrinsic evidence was submitted to the jury, “what is
important to our inquiry is that the trial court’s acceptance
of this waiver was not so offensive to our concept of
ordered liberty so as to shock our conscience”); United
States v. Josefik, 753 F.2d 585, 588 (7th Cir. 1985) (finding
that limitations exist on the ability of parties to stipulate
to the structure of the jury at trial because “if the parties
stipulated to trial by 12 orangutans the defendant’s



2
   (...continued)
through their plea agreement, it is within the realm of our
authority to question, sua sponte, the propriety of doing so. See
Kamen v. Kemper Fin. Servs., 500 U.S. 90, 99 (1991) (“When an
issue or claim is properly before the court, the court is not
limited to the particular legal theories advanced by the
parties, but rather retains the independent power to identify
and apply the proper construction of governing law.”)
18                                             No. 07-1134

conviction would be invalid notwithstanding his consent,
because some minimum of civilized procedure is re-
quired by community feeling regardless of what the
defendant wants or is willing to accept.”).
  Most notably, none of the defendant’s constitutional
rights are infringed by the stipulation and the standard
chosen by the parties is one with which the district court
is familiar. Furthermore, the sentencing hearing was
conducted in a manner that did not substantially deviate
from statutory or constitutional norms, and neither
party has contested the stipulation on appeal. Had any
of these factors not been present, the stipulation might be
invalid.
  The problem is that we cannot determine if the district
court calculated the amounts of drugs attributable to
Hernandez using the reasonable doubt standard. The court
did not explain how it arrived at 159 kilograms as the
drug quantity amount; thus, it is not clear from the
record if the district court acted in accordance with the
stipulation, as it purported to do.


                  III. CONCLUSION
  Accordingly, we R EVERSE and R EMAND this case for
proceedings consistent with this opinion.




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