This paper reports p-rho-T (pressure, mass density, temperature) data measured for a mixture with molar composition (0.95039 methane + 0.03961 ethane + 0.01000 propane) using a high-pressure, single-sinker, magnetic-suspension densimeter (MSD) and high-and low-pressure automated isochoric apparatus at temperatures from (135 to 500) K and pressures to 200 MPa. The composition is representative of a residual natural gas in pipelines, but the range of conditions covers conditions possibly encountered in production and processing. The k = 2 relative uncertainty for the density measurements using the MSD is 5 X 10(-4).rho based upon an uncertainty analysis for the instrument. The isothermal densities measured in the MSD in combination with the low-and high-pressure isochoric data determine additional density data with essentially the same estimated relative uncertainty as the MSD in the high temperature range (above 300 K) and a relative uncertainty of 3 X 10(-3).rho at lower temperatures. The measured densities range from (433.170 to 27.493) kg.m(-3). The GERG-2008 equation of state compares well to the density data. Although the data behave in an expected manner, they cover ranges of temperature and pressure beyond those previously examined. Additionally, the paper describes a new, high-pressure isochoric apparatus as well as a methodology for compensating volume changes and the mass interchanges in the high-pressure cell. The latter technique allows experimental determination of the cell distortion coefficients.