In the winter of 1979/80, five petroleum companies participated in a field test program conducted by Exxon Production Research Company in Prudhoe Bay, Alaska, to measure the unconfined compressive strength of the sea ice sheet in its full thickness at various strain rates between 10−7 and 8 × 10−5 s−1 . As part of this program, ice sample blocks at four different levels in the ice sheet were collected from seven field test sites and shipped to Exxon’s Cold Laboratory in Houston. A total of 221 cylindrical ice samples were made from the ice blocks and tested for their compressive strengths on a closed loop test machine. The sample size was 2.725 in. (6.92 cm) in diameter and 5.75 in. (14.60 cm) long. The strain rate and temperature under which each sample was tested were selected to match actual field test conditions. In addition, 76 thin sections were prepared from tested samples and were studied for the crystallographic structure. Results indicate that local variations of the crystalline structure of the ice sheet could be significant and could cause large variations in the strength of individual samples. The results of the laboratory tests were used to estimate the strength of the full-thickness ice sheet by taking the average value of the through-thickness strength profile. Comparison with field tests shows that this procedure gives very accurate strength estimation for the strain rate range used in the field tests.