"FOREWORD API Standard 2501 supersedes Part 1* of the 7th edition (June 1948) of API Code No. 25: ""Measuring@ Sampling@ and Testing Crude Oil."" This standard has been formulated by@ and represents the unqualified consensus of@ the members?? of the API Committee on Crude-Oil Measurements@ ? who represent all branches of the oil industry which have any interest in the subject matter of this standard with respect to the production@ transportation@ inspection@ storage@ and refining of most of the crude oil in the United States. The purpose of this standard is to unify methods and practices employed in measuring and calibrating crude-oil tanks. In those instances where it has not been possible to obtain national agreement upon a single method or practice@ exceptions are noted and@ in some cases@ alternative methods are described. This procedure is obvious after study of the widely varying conditions under which crude oil is produced and handled in different parts of the country. It is not intended that this standard be retroactive@ nor that it take precedence over contractual agreements. Existing codes and manuals@ whenever practicable@ have been used in the preparation of this standard. Particular credit is given to ASTM Committee D-2@ Division II@ Section E. The American Petroleum Institute takes no position as to whether any method@ apparatus@ or product mentioned herein is covered by an existing patent@ nor as to the validity of any patent alleged to cover any such method. Furthermore@ nothing contained in this standard grants any right@ by implication or otherwise@ for manufacture@ sale@ or use in connection with any method@ apparatus@ or product covered by letters patent; nor does it insure anyone against liability for infringement of letters patent. This standard may be used by anyone desiring to do so@ but the American Petroleum Institute shall not be held responsible or liable in any way either for any loss or damage resulting therefrom or for any violation of any federal@ state@ or municipal regulations with which it may conflict. Note: Only vertical tanks are now covered by Standard 2501. A standard is now in preparation for tank measurement and calibration covering horizontal tanks. A standard on liquid calibration is also being prepared. * Part 2 and 3 of API Code 25 has been superseded by API Standard 2500: Measuring@ Sampling@ and Testing Crude Oil@"" 1st edition@ effective as of Jan. 1@ 1955. ?? The membership of the API Committee on rude-Oil Measurements is recorded in Appendix ""A"" of API Standard 2500 ? Formerly known as Committee on Code 25."