A microfluidic chip for generation of gradients of dissolved oxygen was designed, fabricated and tested. The novel way of active oxygen depletion through a gas permeable membrane was applied. Numerical simulations for generation of O-2 gradients were correlated with measured oxygen concentrations. The developed microsystem was used to study growth patterns of the bacterium Pseudomonas aeruginosa in medium with different oxygen concentrations. The results showed that attachment of Pseudomonas aeruginosa to the substrate changed with oxygen concentration. This demonstrates that the device can be used for studies requiring controlled oxygen levels and for future studies of microaerobic and anaerobic conditions.