During the last few years, two standards for ozone have been developed. One is based on the vapor pressures above liquid or solid ozone, the other is based on the UV light absorption of ozone at the 253.7-nm Hg line. Recent measurements of cross sections at vapor pressures above liquid ozone have provided the correlation between the two standards. The measurements at various vapor pressures resulted, for the 253.7-nm line, in a cross section a room temperature of 1.131¿10-17 cm2 with an rms uncertainty of ¿0.7%. Direct cross-section measurements by simultaneously measuring absolute ozone pressures and temperatures and, in addition, performing a gas purity analysis yielded a cross section of 1.136¿10-17 cm2 with an rms uncertainty of ¿0.5%. The measurements reported show that the two ozone standards agree to better than ¿0.5%. ¿ American Geophysical Union 1987