@TechReport{CEPII:2013-27,
author={Keith Head and Thierry Mayer},
title={Gravity Equations: Workhorse,Toolkit, and Cookbook},
year=2013,
month=September,
institution={CEPII},
type={Working Papers},
url={http://www.cepii.fr/CEPII/en/publications/wp/abstract.asp?NoDoc=6126},
number={2013-27},
}