In Oklahoma criminal cases, a presentence is a court-ordered report compiled by the Department of Corrections. 22 O.S. §982 sets forth a requirement that prior to sentencing on any "violent offense" (with a list of the particular offenses, which does not happen to include every offense I would consider to be violent) the Oklahoma Department of Corrections will conduct an investigation "into the circumstances of the offense and the characteristics of the offender". This report can be waived by the offender. For nonviolent offenders the statute requires that upon their second conviction but prior to sentencing such a report will be produced by a "private provider or someone designated by the court". In practice this has also been the Department of Corrections.
Essentially the DOC (through a probation officer typically) reads a summary of the police reports and materials (such as health records) submitted by the offender or requested by the Court. In addition, they interview the victims (if any) and the offender. Having compiled whatever information they got from all this they then write a short, structured report that includes a summary of what they found out. They finish out the report with a recommendation. 90% of the time the report states that incarceration would be appropriate. Occasionally it does not and recommends a diversion program such as Community Sentencing or another form of probation.
The right attorney can make this process work in your favor (depending, obviously, on the facts of your case, i.e. if you plead to first degree robbery wherein you are alleged to have shot someone a presentence investigation is unlikely to help you no matter who your attorney might be). However, you can request a pre-sentence investigation in circumstances that they aren't usually called for in (such as a first non-violent felony). We have done this when the government's position was that a non-violent offender should be incarcerated for a first offense and had success. Would it work in another case? You would have to consult with your counsel and weigh your options carefully for in order to employ this strategy one must first plead guilty to the offense.
If you are facing sentencing for a serious crime and need advice call a criminal defense attorney at (405) 310-9890 for a free consultation.