The introduction of competition in regulated industries may have positive or negative side-effects on the provision of collective goods or services. The paper shows that these effects are closely related to two associated elements: the industrial strategies developed by utilities and the regulatory environment within which they operate. Regulatory rules and corporate strategies influence the treatment of public service obligations. This raises a major issue regarding the regulation of public utilities. To reduce the drawbacks of the introduction of competition, it is necessary to set regulatory rules that allow the implementation of market configurations enabling public utilities to follow a public service orientation rather than a pure market-based approach. © CIRIEC 1999.