The foundations of compliant structures are subjected to a large magnitude of tension and a superimposed cyclic load. Pile foundations are more suitable for this type of structure. In this paper, the behavior of longer pile groups under uplift is studied by conducting tests on model pile groups made with steel pipes. The tests are conducted in a marine clayey soil bed prepared in a test tank at a soft consistency. Tests on pile groups were conducted at three embedment lengths of 15d, 25d and 40d. At each embedment length, the spacing of piles are varied from 2.5d to 15.0d. From the test results, it is found that the efficiency of pile groups under uplift depends upon the spacing of piles, embedment length of piles and number of piles in a group. For a pile group with an L/d of 15, 100% efficiency is attained at an S/d value of 7.5. For higher L/d values of 25 and 40, nearly 100% efficiency is reached at an S/d of 9-10. In the range between 60 and 100%, the L/d ratio affects the efficiency values substantially. The efficiency values obtained are compared with the reported values in the literature and are in good agreement. The validity of the methods that are being used to compute the efficiency of pile groups under compression is examined for the pile groups under uplift. © 1994.