  I derive the physical properties of 30 transiting extrasolar planetary
systems using a homogeneous analysis of published data. The light curves are
modelled with the JKTEBOP code, with attention paid to limb darkening and
eccentricity. The light from some systems is contaminated by faint nearby
stars, which if ignored will systematically bias the results. I show that this
must be accounted for using external measurements of the amount of
contaminating light. A contamination of 5% is enough to make the measurement of
a planetary radius 2% too low. The physical properties of the 30 transiting
systems are obtained by interpolating in stellar model predictions to find the
best match to their measured quantities. The error budgets are used to compile
a list of systems which would benefit from additional observations. The
systematic errors arising from the inclusion of stellar models are assessed by
using five different theoretical models. This model dependence sets a lower
limit on the accuracy of measurements of the system properties, and at worst is
1% for the stellar mass. The correlations of planetary surface gravity and mass
with orbital period have significance levels of only 3.1 sigma and 2.3 sigma.
The division of planets into two classes based on Safronov number is
increasingly blurred. Most of the objects studied here would benefit from more
photometry and/or spectroscopy, as well as a better understanding of low-mass
stars.
