During February 1982 a NOAA research aircraft investigated a cold, low-level jet blowing from a gap between mountain ranges on line west side of Cook Inlet, Alaska. The jet blew 200 km southeastward across Cook Inlet between the Kenai Peninsula and the Kodiak archipelago, passing into the Gulf of Alaska where it merged with the large-scale marine wind field. Measurement commenced ∼35 km downstream of the seaward end of the gap. The jet's internal boundary layer accelerated by 5% and grew 20% in depth for ∼50 km; thereafter, wind speed and boundary-layer depth were nearly constant for the next 100 km. The strongest winds (>20 m s−1 at a height of 80 m) were observed on the south side of the jet's thermal axis and 90 km downstream from the coast. Budget analyses reveal that the down-gradient acceleration within the jet was principally opposed by surface friction, and the cold air advection was balanced by a strong upward-directed sensible heat flux from Cook Inlet and entrainment of warmer air from aloft.