A desire to increase liquidity of PetroChina shares was behind the decision to grant a strategic shareholders' request to sell some of their holdings before the lock-up period expired.

The shareholders have been allowed to sell up to 30 per cent of the shares although the six-month lock-up period does not expire until October 7.

The move was approved by PetroChina's global co-ordinators as they believed it would reduce price volatility in light of its low free float, a source said.