Landing at Stokes's Treachery Bay, Gregory and his brother Frank explored Stokes's Victoria River to its sources, and found another watercourse, whose waters, running inland, somewhat revived the old theory of the inland sea.

Upon tracing this river, which he named Sturt's Creek, after the father of Australian exploration, it was found to exhaust itself in a circular basin, which was named Termination Lake.
Retracing the creek to where the depot was situated, the party travelled across a stretch of unknown country for some two hundred miles, and striking Leichhardt's Port Essington track on Leichhardt's Roper River, his route was followed too closely for hundreds of miles until civilisation was reached.

My friend Baron von Mueller accompanied this expedition as botanist, naturalist, surgeon and physician.
Soon after his return from his northern expedition, Gregory was despatched in 1858 by the Government of New South Wales to search again for the lost explorer Leichhardt, who had then been missing ten years.

This expedition resulted in little or nothing, as far as its main object was concerned, one or two trees, marked L, on the Barcoo and lower end of the Thompson, was all it discovered; but, geographically, it settled the question of the course of the Barcoo, or Mitchell's Victoria, which Gregory followed past Kennedy's farthest point, and traced until he found it identical with Sturt's Cooper's Creek.

He described it as being of enormous width in times of flood, and two of Sturt's horses, abandoned since 1845, were seen but left uncaptured.