This work presents reliable measurements for dynamic viscosity of representative heavy oil samples from Mexican reservoirs. Most of the experimental data of dynamic viscosity were measured using a constant force electromagnetic viscometer. The viscometer was calibrated using several viscosity standards based on a maximum standard deviation of 0.5% in all measurements for the three pistons used. Dynamic viscosities of heavy dead crude oils were obtained at a temperature range from 397.1 to 300.8K, viscosities in the range of 10.9–7476.7cP, oil API gravity from 11.5 to 19.4, and at a constant pressure of 0.1MPa. The estimated uncertainty on viscosity was less than ±1.0% over the temperature range of measurements. A new correlation approach was developed to estimate dynamic viscosities of Mexican heavy crude oils based on oil API gravity, and temperature.