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Results of a comprehensive series of fracture toughness tests on oil shale from Anvil Points are presented. Since oil shale is layered and transversely isotropic, three-point-bend specimens representing 20 and 40 gal/ton were tested in the three principal crack orientations--divider, arrester, and short transverse. These specimens were fatigue cracked to produce a sharp natural crack in a stable manner by means of loading between fixed limits of the crack opening displacement. Crack front position was marked by immersing the specimen in a penetrating dye so that the crack length could be determined after final failure. Load-to-failure records of load vs. crack opening displacement showed evidence of crack surface interference or crack closure. Fracture toughness was found to decrease by approximately 40 percent for an increase in kerogen content from 20 to 40 gal/ton. Highest values of fracture toughness were found for the divider geometry, lowest for short transverse, and intermediate for arrester with the actual values varying from 0.3 to 1.1 MN m/sup - exp 3 / sub 2 . (ERA citation 02:035808)