A downhole liquid-gas separator for use with a submergible pump employs an inverted conical, convoluted, fine-mesh screen in a tubular housing. The convolutions form grooves extending upwardly along the screen. A liquid-gas mixture enters the housing near the lower, apex end of the screen. The screen mesh size is selected so that liquid is pumped through the screen and continues to flow upwardly through the housing, while gas bubbles rise along the exterior of the screen and are vented from the housing. The gas bubbles channel into the troughs of the screen grooves, leaving the peak regions of the convolutions free for the passage of liquid. A relief valve arrangement bypasses the screen when it becomes clogged, and permits the liquid-gas mixture to flow upwardly through the housing.