Extracts of samples from cores of Tertiary strata at six sites off the Atlantic coast of northern Florida and across the Blake Plateau contained very meager quantities of hydrocarbons and other soluble organic material. Eleven samples forming a group with the least carbonate content from the shelf and continental slope were available for hydrocarbon analyses. In five of these samples from depths less than 25 m below the ocean floor, the smaller molecular sizes, ranging from C (sub 12) to C (sub 20) averaged 22.1 percent of the saturated hydrocarbons (C (sub 12) -C (sub 30) ), whereas in the remaining six samples from greater depths, this fraction averaged 36.5 percent.