Mustard oil prices softened by Rs 50 per quintal in an otherwise steady wholesale oils and oilseeds market owing to sluggish local demand. Castor oil in the non-edible section, also eased on reduced offtake by consuming industries. Sluggish demand from local parties, mainly weighed on mustard oil prices. National Commodity and Derivative Exchange, mustard seed to be delivered in January declined 0.62 per cent.The delivery for the most-active February fell 0.53 per cent, clocking an open interest of 34,640 lots.