api36API gravity express the gravity or density of crude oil and liquid petroleum products. API is devised jointly by the American Petroleum Institute and the NIST - National Institute ofAPI CASING TABLE SPECIFICATION Size Wei ght ID Drift Capacity Inches mm lbft Inches mm Inches mm bbl100ft 7 34 196.85 46.10 6.560 166.62 6.500 165.10 4.18