KUWAIT- Saudi Aramco's downstream profit lagged major rivals in the first half of 2017, Bloomberg reported on Monday.

Aramco made almost all of its profit in upstream during the period, with downstream delivering just $842 million in net income, compared with a loss of $484 million in the first half of 2016, Bloomberg said, citing accounting data.

By comparison, Shell made $5 billion from refining and chemicals in the first half of 2017 and Exxon $4.7 billion.

The financial data did not explain why Aramco trailed other oil firms in downstream, Bloomberg said.

Last week the news agency reported that Aramco, the world's biggest oil producer, had net income of $33.8 billion in the first six months of 2017 and cash flows of $52.1 billion.

Aramco's financial performance has long been one of the best kept secrets in the oil industry but as it prepares for a planned initial public offering (IPO) this year or next it will have to tell investors what it earns and how it operates.

Aramco pumps about 10 million barrels per day (bpd) of crude oil and plans to raise its refining capacity to between 8 million to 10 million bpd from around 5 million bpd now.

Aramco wants to become more diversified to boost its valuation and attract IPO investors. The listing is a centrepiece of a plan championed by Crown Prince Mohammed bin Salman to diversify Saudi Arabia's economy beyond oil.

(Reporting by Rania El Gamal; Editing by Ghaida Ghantous and Alexander Smith) ((rania.elgamal@thomsonreuters.com; +971 562 160 434; Reuters Messaging: rania.elgamal.reuters.com@reuters.net ; Twitter: https://twitter.com/Rania_ElGamal))