With much of the reservoir engineering development activities prior to 1986 being directed to new processes such as EOR, reservoir engineering of today has, like the other petroleum engineering disciplines, become part of an integrated effort to extract the maximum amount of oil from a reservoir. We will discuss some of the new developments in reservoir engineering which had a real impact on oil field operations in Shell and on the working practices of the individual reservoir engineer. Examples of recent advances in reservoir engineering are: (1) progress in the field of measuring residual oil saturations to water under representative conditions which will enable a more realistic assessment of trapped/bypassed oil in water floods such as those in large North Sea fields; (2) improved understanding of the production behaviour of horizontal wells based on analytical and numerical modelling which led to successful applications in Gabon and Oman; (3) advances in our understanding of production in naturally fractured reservoirs which provided the basis for a unique field experiment in the Natih Field in Oman; (4) understanding of the mechanism of fracturing in water injection wells, a process which has large cost-saving potential. The one factor largely responsible for the change in working practices of individual reservoir engineers is the availability of modern integrated IT technology. Moreover, working with uncertainty in a structured way has become routine in a reservoir engineer's work.