A new piece of equipment was developed for testing catalytic cracking and catalyst regeneration, particularly for short contact times. The gas oil to be cracked is injected into the upper section of the reactor, which can be operated in the temperature range 400-800 degrees C, catalyst-to-oil ratios from 0 to 300 g(cat)/g(oil) and residence times between 0.01 and 2.3 s. The product is led directly into the analysis section where hydrocarbons from C-1 to C-12 (in total 350 compounds) are separated by a capillary column. In catalyst regeneration studies oxygen/nitrogen pulses are fed into the reactor via a gas-loop. The carbon monoxide and carbon dioxide formed are first separated in a packed column after which they are converted to methane by hydrogen on a Ni/gamma-Al2O3 catalyst ensuring the determination of even small amounts of coke. The reproducibility of the experiments has proved to be excellent. With this new reactor system, accurate information can be obtained on the initial activity of the catalyst and product distribution.