The purpose of the IOGP S-613 specification documents is to define a minimum common set of requirements for the procurement of air dryer packages for application in the petroleum and natural gas industries. The IOGP S-613 specification documents follow a common structure comprising a specification, also known as a technical requirements specification (TRS), a procurement data sheet (PDS), an information requirements specification (IRS) and a quality requirements specification (QRS). These four specification documents, together with the purchase order, define the overall technical specification for procurement.