The specific heat of a large YBa2Cu3O6.92 single crystal (m approximat
e to 150 mg) was measured between 0 and 27 Tesla. In contrast with pre
vious results obtained at lower fields, the specific heat above T-c is
field-dependent up to 100 K. The high magnetic fields combined with a
narrow transition width (Delta T-c(10-9%)=0.15 K in ac susceptibility
) allow an accurate analysis of the different contributions in the vic
inity of T-c(H=0). 2D-3D gaussian and 3D-xy critical fluctuations mode
ls are compared. A positive curvature of the H-c2(T) line is observed
up to 10 Tesla. The compatibility of the calorimetric and magnetic mea
surements [1] through Maxwell's relation is also verified.