261 oil and 680 gas reservoirs have been explored within the territory of Hungary. Their depths and pressures range from 300 to 4500 m (1,000 to 15,000 ft) and from 3 to 85 MPa (430 to 12,000 psi), respectively. The highest temperature ever measured during our reservoir voir test operations was 218.3 degrees C (425 degrees F) at 4550 m depth in Well L-II. (1973). Some of the testing methods elaborated during the exploration and development of this large amount of reservoirs can be of international interest; the fill-up procedure, providing pressure buildup (PBU) curves equivalent to those of bottomhole shut-in tests in low-production oil and gas wells, is one of them. The paper presents and analyzes the results of 497 fill-up PBU tests with particular attention to the impacts of reservoir ''reworkings'' (retesting,acidizing, fracturing, horizontal drilling).