Abstract: A hydraulic well jar mechanism capable of developing jarring force in an upwardly or downwardly direction or in both upward and downward directions for imparting jarring forces to stuck well pipe. Inner and outer tubular members cooperate to define an annulus therebetween, which annulus contains a volume of metering liquid such as oil. One or more metering valves are disposed within the annulus and establish metering of the metering liquid during a portion of the stroke of the well jar to thus retard movement thereof. After a certain metering movement has occurred, the operative metering valve will be clear of the metering surface and the jar mechanism will then have relatively free movment from the retarded position to the jarring position. Closing movement of the jar mechanism may be induced by a compression spring closure.