API比重

API用来表示石油流体相对于水的比重，定义为API=\frac {141.5}{\bar{\gamma_{o}}}-131.5，其中\bar{\gamma_{o}}是60^\circ/60^\circ时油的\bar{\gamma}值。

液体的\bar{\gamma}值，定义为同一温度和压力下液体密度\rho与水的密度\rho_{w}之比。

若API大于10，石油液体密度小于水。正常情况下大多数石油流体API值介于10到70之间。
参考文献
外部链接
*[http://www.koehlerinstrument.com/products/hydrometer.html Link to hydrometer]
*[https://web.archive.org/web/20140728125404/http://dnr.louisiana.gov/assets/docs/oilgas/productiondata/comments_1989_rev.pdf Comments on API gravity adjustment scale]
*[http://www.globalsecurity.org/military/library/policy/army/fm/10-67-1/APPI.HTML Instructions for using a glass hydrometer measured in API gravity]
*[http://www.sizes.com/units/hydrometer_api.htm API Degree history]