Defendant pleaded guilty to six criminal charges: first degree rape, second degree rape, aggravated burglary, forcible sodomy, and two counts of aggravated sexual assault. The trial court was required to impose minimum mandatory prison terms for the aggravated sexual assault convictions under Utah Code Ann. § 76-5-405(2) (Supp.1983) (amended 1986). Prior to sentencing, defendant challenged the constitutionality of the minimum mandatory sentencing provisions. The trial court denied defendant’s motions and imposed a fifteen-year minimum mandatory sentence for *559each count of aggravated sexual assault and indeterminate sentences for each of the six charges, all terms to run concurrently. Defendant appeals from the mandatory sentences.
Defendant was originally charged with twenty-two criminal offenses. In exchange for the dismissal of all other charges, he pleaded guilty to the offenses described in the preceding paragraph. No facts beyond the names of the victims, the dates of the alleged offenses, and the statutory definitions of the alleged offenses are discernible from the record. Defendant submitted to the trial court a statement of apology and two letters indicating his need for and amenability to treatment. This was the only evidence submitted to that court regarding aggravation or mitigation. The trial court did not explain at length the factors entering into its sentencing decision, although the judge made the following comments at the sentencing hearing: “I have gone over the letter that [defendant] submitted as to these offenses ... and there are five rape cases, forcible rapes. Under any standard I think the maximum should apply in this case, and I am taking that into consideration_”
Defendant argues that the minimum mandatory sentencing scheme under which he was sentenced violates equal protection principles, constitutes cruel and unusual punishment, and runs afoul of Utah’s constitutional separation of powers doctrine. He also contends that the statutory scheme is unconstitutionally vague. The issues raised by defendant's first three arguments have been resolved in favor of plaintiff by our decision in State v. Bishop,1 in which we upheld Utah Code Ann. § 76-5-403.1(2) (Supp.1987) (minimum mandatory sentencing required upon conviction of sodomy on a child). We therefore do not treat those arguments further.2 We have not yet, however, analyzed the minimum mandatory sentencing scheme in terms of a challenge for vagueness.3
“It is a fundamental tenet of due process that ‘[n]o one may be required at peril of life, liberty or property to speculate as to the meaning of penal statutes.’ ”4 This principle is applicable to sentencing as well as substantive provisions of criminal statutes.5 In United States v. Batchelder,6 the United States Supreme Court pointed out that “vague sentencing provisions may pose constitutional questions if they do not state with sufficient clarity the consequences of violating a given criminal statute.”7
Any vagueness to be found in subsection 76-5-405(2), which provides for sentences of five, ten, or fifteen years and which may be for life, is dispelled by the implementing language of Utah Code Ann. § 76-3-201(5) (Supp.1983) (amended 1984, 1986 & 1987), which plainly mandates imposition of the sentence of middle severity unless there are circumstances in aggravation or mitigation of the crime. It is also plain from that statute that imposition of the sentence of highest severity is dependent upon a determination of the existence of aggravating circumstances, while imposition of the sentence of lowest severity is dependent upon a determination of the existence of mitigating circumstances.
There is nothing equivocal about the provisions of section 76-5-405. The commission of a prohibited sexual act that is ac*560companied by an aggravating circumstance of bodily injury, use of or threat with a deadly weapon, or threat of kidnapping, death, or serious bodily injury is punishable by imprisonment for a minimum mandatory term of five, ten, or fifteen years. Upon conviction, subsection 76-3-201(5) comes into play, and it is likewise couched in unequivocal language. It mandates “imposition of the term of middle severity unless there are circumstances in aggravation or mitigation of the crime.” Thus, it is clear that although a listed aggravating circumstance is an essential element of the crime of aggravated sexual assault, one convicted of that crime nevertheless cannot be sentenced to a mandatory term greater than that of middle severity in the absence of additional aggravating circumstances.
In this case, the evidence offered in mitigation was meager. It consisted of a statement of apology for defendant’s actions and two letters indicating his need for and amenability to treatment for his behavior. In contrast, the existence of additional aggravating circumstances was significant.
The record reflects that the trial judge duly considered the aggravating and mitigating circumstances. At the time of sentencing, he stated his reasons for imposing concurrent sentences of highest severity as follows: “I have gone over the letter that [defendant] submitted as to these offenses ... and there are five rape cases, forcible rapes. Under any standard, I think the maximum should apply in this case, and I am taking that into consideration. ...” He thus did not abuse the discretion in sentencing afforded by the statutes.
The decision the statute required the trial court to make in imposing one of three alternative mandatory sentences did not differ from other decisions made daily on whether to impose indeterminate sentences, to suspend sentences, or to place offenders on probation.
The judgment and sentence of the trial court are affirmed.
STEWART, Associate C.J., and HOWE, J., concur.. 717 P.2d 261 (Utah 1986).
. For analytical purposes, sentencing under Utah Code Ann. § 76-5-405(2) (Supp.1983) (amended 1986) and Utah Code Ann. § 76-5-403.1(2) (Supp.1987) is identical except for the length of the minimum mandatory terms.
. Defendant has relied only on federal constitutional principles in his analysis of the vagueness question. Therefore, our analysis treats only federal law. See State v. Earl, 716 P.2d 803, 805 (Utah 1986).
. United States v. Batchelder, 442 U.S. 114, 123, 99 S.Ct. 2198, 2203-04, 60 L.Ed.2d 755 (1979) (quoting Lametta v. New Jersey, 306 U.S. 451, 453, 59 S.Ct. 618, 619, 83 L.Ed. 888 (1939)).
. See id.
. 442 U.S. 114, 99 S.Ct. 2198.
. Id. at 123, 99 S.Ct. at 2203-04 (citations omitted).