Indian budget airline SpiceJet has agreed to buy about 40 Boeing 737 jets worth over $4 billion at list prices, industry sources said, a move that could help the loss-making carrier as it seeks new investors.

The deal includes a firm order for as many as 42 Boeing 737 MAX aircraft that offer fuel savings compared to SpiceJet's existing fleet of current-generation Boeing 737s, sources said.

Such an order would be worth $4.4 billion at list prices without adjusting for either inflation or price discounts.

The Indian carrier has also negotiated options to double the order by taking up to 42 further jets depending on its ability to grow. A spokeswoman for SpiceJet declined to comment.

On Monday, Boeing said unidentified airlines had placed orders at the end of 2013 for 164 such medium-haul aircraft.

Sources said at least part of the SpiceJet order is included among those latest unidentified orders and is therefore already part of Boeing's backlog of new business.

The deal comes as India's fourth-biggest airline by domestic market share seeks new planes and new investments to revive its fortunes after posting a record quarterly loss in November, hit by costly fuel and a weak rupee.-Reuters