The difference between the two programs is this:
An Offer in Compromise is for taxpayers who owe a significant amount of money to the IRS, but can’t pay this debt, even over time. Sometimes, the IRS allows the taxpayer to make an offer that would settle that debt once and for all. Often this offer amounts to a substantial discount.
A negotiated Installment Agreement is for taxpayers with debt who are unable to pay the debt off in one lump sum, but who will have the resources to pay the debt down over time. The taxpayer makes monthly payments to eliminate the tax debt.