Comprehensive (p, rho, T) measurements on pure ethane have been carried out in the single-phase region (369 values) and along the entire (vapour + liquid) coexistence curve (118 values). The results reported in this first paper cover the homogeneous gas and liquid regions in the temperature range from 95 K to 340 K at pressures up to 12 MPa. The total uncertainty of the measurements in density is +/-(0.015 to 0.022)% with the exception of the critical region for temperatures from 298 K to 318 K (T-c = 305.322 K) at densities between 120kg . m(-3) and 280kg . m(-3) where the total uncertainty in pressure is +/-(0.006 to 0.016)%. Values for the second and third virial coefficients have been determined from the measurements in the homogeneous gas region of ethane. The experimental results are compared with previous results of other workers.