The study draws upon expectancy theory and proposes a reverse relationship between rewards, knowledge sharing, and job performance. Knowledge sharing behaviours including knowledge donation, collection, and lurking are modelled to intervene between this relationship. The study was conducted with employees who had used online knowledge platforms in organisations from three industries in Vietnam, namely, tele-communications, banking, and insurance. A pilot study was undertaken prior to the formal survey to ensure clarity and validity of the questionnaires. The results show that job performance was significantly related to knowledge donating and collecting but not related to lurking. Knowledge donating, collecting, and lurking also have a significant impact on intrinsic rewards respectively and that top management support moderates the effect of knowledge donating, knowledge collecting, and lurking on intrinsic rewards. The study extends expectancy theory into online knowledge sharing literature and suggest for optimising organisational resources and maximising knowledge sharing values.