PurposeThis paper investigates the influence of employees’ extra-role and in-role behaviours on customer service alongside the moderating role of gender.Design/methodology/approachThis paper employs the theory of behavioural intentions, cross-sectional survey design and quantitative approach to collect the data from 426 purposively sampled workers and customers of oil marketing companies. The data were analysed using descriptive statistics, correlation and the hierarchical regression model in SPSS.FindingsThe results indicate that employees’ extra-role behaviour has a significant positive effect on customer service while employees’ in-role behaviour has no significant effect on customer service. It is also established that gender of staff can significantly moderate the relationship between extra-role behaviour and customer service such that the behaviour of female staff has greater effect on customer service than their male counterparts. However, the gender of staff has no moderating effect on the relationship between in-role behaviour and customer service.Practical implicationsThe findings imply that female staff should be allowed to directly engage customers more often than male staff to promote superior customer service. Managers should continuously improve upon the behaviour of employees through orientations, workshops and mentoring. Behaviour stimuli such as awards, appreciations and recognition for best workers would have to be encouraged to induce employees to act beyond their prescribed-roles.Originality/valueThis study is the first to investigate how staff behaviours (in-role and extra-role) impact customer service, with gender of the employees as a moderator. This paper contributes to literature by empirically confirming the differential influence of employees’ extra role and in-role behaviours on customer service and the effectiveness of gender as a moderator on the relationship between extra-role behaviour and customer service from a developing country perspective and an industry where there is dearth of research.