Mumbai: The rupee gained 39 paise to 84.18 against the US dollar in early trade on Monday, as continued foreign investor interest in Indian assets lent fundamental support to the local unit. Forex traders said a sharp decline in crude oil prices and a positive trend in domestic equities enthused investors further. Brent crude oil prices slumped nearly 4 per cent in the morning Asian trade after OPEC+ signalled over the weekend that they will further increase production in the coming month