Understanding GSA Modification Number Codes

By Global Services on July 20, 2018

If you’re a GSA Schedule holder, you’ve probably seen a Standard Form 30, contract modification form, or contract modification number. Contract modification forms are useful to understand the changes or potential changes of a contract but also in understanding how to capture or even obtain information on a competitor’s contracts. These mods are assigned an identifying number such as PS-0001 or PO-0011. The numerical portion of this sequence is straightforward: the first mod to your contract is 0001, the next is 0002, and so on. But the meaning of the two-letter code that begins each mod number is less readily apparent. Below we outline this coding system, so that you can readily identify what type of mod you’re viewing.

Contract Modification

The Two-letter Coding System

The two-letter coding system is derived from the Federal Acquisition Regulations (FAR) Part 43, and works as follows:

The First Letter

The first letter will be either a P or an A. This indicates whether the mod is coming from the Procuring Contracting Officer or the Administrative Contracting Officer. (Note: some Schedules, such as the Professional Services Schedule (PSS), no longer have Administrative Contracting Officers, so all mods under these schedules will begin with P).

The Second Letter

The second letter will be either an A, an S, or an O. These indicate the type of mod: Administrative, Supplemental, or Other.


Administrative type mods include changes to your company address, authorized negotiators, points of contact, phone number, and so on. These mods are unilaterally executed by the Government.


Supplemental type mods include changes to Economic Price Adjustment; adding/removing Special Item Numbers (SINs) or products/services from a contract; revisions to terms and conditions; service description changes; addition of subcontracting plans; and so on. These mods are governed by 552.238-81 Modifications (Federal Supply Schedule) (APR 2014), and require both the Government and the contractor to agree to the modification in order to take effect.


Other type mods include cancellations, terminations, options, and novation or change of name agreement mods. These mods are unilaterally executed by the Government. In the case of cancellations, this means that contractors can request a cancellation and the Government will unilaterally execute the cancelation mod based on that request. Novations and change of name agreements must be requested by the contractor and are subject to Government approval; if approved, the Government will unilaterally execute the mod.

Finally, note that the numerical portion of the mod number counts up in order, regardless of the alphabetical prefix. That is, your first mod could be PA-0001, your second PS-0002, your third AO-0003, and so on.

Have questions about modifications to your Schedule? Contact Global Services today for additional information and assistance!