We establish the context of maintenance outsourcing of mission critical applications by Fortune 500 organizations. We present the results of empirical studies that were conducted at Syntel, a NASDAQ listed application management and e-business solutions company, on 46 software maintenance projects that belonged to various lines of business on the IBM mainframe platform using an automated data collection tool EQUIP. After establishing that corrective maintenance activities form a significant component of the overall maintenance efforts, we examine the applicability of the IEEE standard maintenance process for corrective maintenance by measuring the efforts spent on the various activities. We conclude that a) the processes for each type of maintenance need to be fine tuned especially in the context of outsourcing b) analysis, testing form significant part of the corrective maintenance effort c) teams need to carry out other activities such as database reorganization and configuration management that are not defined by the IEEE maintenance process.