The position of the water table around an oil or gas accumulation may be affected by various constraints, both geological and physical. In the complete absence of geological constraint, the table is still not likely to be horizontal, except where the average pore size in the sand is uniform all around the pool. If the average pore size is much greater at the north end of a pool, for example, than at the south end, the result of capillary forces will raise the water table at the south end with respect to the level at the north end. A simple picture of this effect is obtained by considering the following experiment. In a vessel of water, set up a ring of vertical capillary tubes of bore proportional to the mean grain size at each point along the ring representing the oil-wa er interface. The position of the top of the water columns in these capillaries will then represent the water table tilt to be expected around the pool. The paper gives the required mathematics and a numerical application to a California pool with known water table tilt.

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