We carried out a quantitative spectral analysis of 73 hot subluminous O-stars selected from the SDSS spectral database .
While the helium deficient sdOs are scattered over a wide range of effective temperature and gravity , the helium enriched sdO stars are concentrated in a small intervall of 40 kK to 50 kK and \log g = 5.5 \ldots 6.0 .
Comparing the distribution in the T _ { eff } - \log g -diagram with evolutionary tracks , we find the helium deficient sdOs to be the progeny of the sdB stars .
The results for the helium enriched ones are less conclusive .
Both the merger of two white dwarfs and the delayed helium core flash scenarios are viable options to be explored further .