Post-implementation support for information systems (ISs) remains an important but under-explored topic. In this study, we focus on the customer service aspect of post-implementation support for enterprise resource planning (ERP) systems and examine the antecedents and performance consequences of customer-oriented organizational citizenship behaviors (OCBs) performed by information technology (IT) personnel. We predict that characteristics of IT support tasks influence IT personnel's customer-oriented OCBs, which in turn exert both direct and moderating effects on their task efficiency. The analysis of 300 support tickets in relation to two ERP modules (Supplier Relationship Management and HR/Payroll Management) in a large enterprise provides mixed results. Task type was found to be associated significantly with the occurrence of OCBs, but the influence of task complexity was not significant. Moreover, OCBs were found to be negatively related to task efficiency, but the degree of the negative relation was contingent on task type and task complexity. The findings enhance our understanding of IT support services and extend the OCB literature on customer orientation. Practically, the results offer insights into managing IT support and IT workforce during the post-implementation stage of information systems.