Retrograde condensation

The formation of liquid hydrocarbons in a gas reservoir as the pressure in the reservoir decreases below dewpoint pressure during production is called retrograde condensation

The diagram below demonstrates the phenomena of retrograde condensation. For a pure component, as we reduce pressure from within the gas phase, we only produce more gas. We never evolve a liquid.
In retrograde condensation however, reducing the pressure below the dew point evolves more and more liquid (see movement from point 1 to point 2). As we continue to reduce pressure, the process reverses itself, and we form less and less liquid until we hit the dew point again, and are back to all gas (see movement from point 2 to point 3).