  We present results on the equation of state in QCD with two light quark
flavors and a heavier strange quark. Calculations with improved staggered
fermions have been performed on lattices with temporal extent Nt =4 and 6 on a
line of constant physics with almost physical quark mass values; the pion mass
is about 220 MeV, and the strange quark mass is adjusted to its physical value.
High statistics results on large lattices are obtained for bulk thermodynamic
observables, i.e. pressure, energy and entropy density, at vanishing quark
chemical potential for a wide range of temperatures, 140 MeV < T < 800 MeV. We
present a detailed discussion of finite cut-off effects which become
particularly significant for temperatures larger than about twice the
transition temperature. At these high temperatures we also performed
calculations of the trace anomaly on lattices with temporal extent Nt=8.
Furthermore, we have performed an extensive analysis of zero temperature
observables including the light and strange quark condensates and the static
quark potential at zero temperature. These are used to set the temperature
scale for thermodynamic observables and to calculate renormalized observables
that are sensitive to deconfinement and chiral symmetry restoration and become
order parameters in the infinite and zero quark mass limits, respectively.
