The maximum force generated by ice sheets moving against stationary structures is a function of the strength of the ice in the relevant mode of failure. For cylindrical structures, as might be used for offshore drilling in the Arctic, the ice fails in crushing. Knowledge of the ice crushing strength is therefore a prerequisite for safe and economical exploitation of arctic offshore resources. In 1969, Imperial Oil Ltd, on behalf of several oil companies, conducted a series of in situ ice crushing tests in the Mackenzie delta area of the Beaufort Sea. By means of a novel technique, cylinders up to 150 cm in diameter were pushed through the ice to measure the ultimate pressure that arctic ice can exert on cylindrical structures. Ice crushing strengths from 4 x 10 to the 6th power to 6 x 10 to the 6th power newtons/meter were measured. Tests conducted with the larger diameter cylinders yielded the lowest ice crushing strengths. The measured ice crushing strengths were higher than anticipated, but it is believed that they represent maximum values for the particular conditions of the tests. One condition was that the ice was frozen to the test cylinders prior to each test. The significance of the results are discussed in relation to the design of offshore structures for the Beaufort Sea.