PSA, Renault, Gaz de France and TNO carried out a joint research programme with the aim to develop a CNG vehicle based on a Citroën BX 19 GTI. In order to make optimal use of CNG a optimized engine concept (increased compression ratio) was adopted.The paper describes the engine testbed work, the vehicle body modifications and the initial vehicle testing. By increasing the compression ratio from 9.3:1 to 11.5:1 the power loss of the engine when running on CNG could be limited to approx. 16%. When running on petrol a similar power loss was observed.Emissions complied with the 91/441/EEC regulation (CO: 18.9%; HC + NOx = 53.6%).Software developed by TNO specifically for this purpose enabled TNO the make use of only one control unit (EFI-4 of Delco Electronics Inc.) to perform engine management functions for both fuels.A good driving range is obtained with a minimum loss of boot space.