Making PCI Stand For Coordination & Impact : Daniel Wallace

Onsite PCI assessments are not cheap. First make certain that you have to comply with the onsite assessment requirement.

Although all of the major card brands are partners in PCI-DSS the number of transactions are counted by individual card brand.

For example, a merchant that processes 2 million credit card transactions will not necessarily be a Level 2 retailer. What matters for purposes of this requirement is the number of MasterCard transactions. You may have 800,000 MasterCard transactions, 600,000 Visa transactions, and 600,000 transactions with American Express.

via Making PCI Stand For Coordination & Impact : Information Security Resources.