Saudi Aramco has asked banks to submit proposals for an advisory role for its initial public offering (IPO) as the top global oil exporter prepares for the biggest ever public share sale in the world.

The US-based Goldman Sachs and the UK’s HSBC are among the lenders to submit pitches. Aramco’s request for proposals has also gone out to banks including Switzerland’s Credit Suisse and the US’ Morgan Stanley, according to news agency Bloomberg, which cited sources familiar with the matter.

Aramco, which has been the main revenue-earner for Saudi Arabia over the past eight decades, is targeting the second half of the 2018 for its IPO and will award formal mandates later this year.

The US’ JPMorgan and advisory firm owner Michael Klein have already been selected for the deal. Klein is providing strategic advice to the government, while JPMorgan is working on preparations for the transaction and may be among the banks that underwrite the listing, according to the report.

Riyadh aims to list less than 5 per cent of Aramco, which is estimated to be valued at more than $2 trillion. The $100bn in proceeds from the share sale would make it the biggest in the world, dwarfing the $25bn raised by Chinese internet retailer Alibaba in 2014.

Aramco CEO Amin Nasser said in October that the oil and gas giant will “very soon” announce a list of investment banks and consultants for the IPO. The public offering would cover Aramco’s entire business and not just distribution and refining operations, he said at the time.

Saudi Arabia aims to list the company on the Saudi Stock Exchange (Tadawul) and one or two as yet unnamed international bourses.

Aramco is at the heart of Saudi Arabia’s economic diversification plan, which includes the privatisation of state assets. The measures include reducing subsidies, introducing taxes, spending cuts and increasing and introducing new fees on government services to generate alternative revenue lines.

The report said Aramco did not immediately return calls. Representatives for Morgan Stanley, HSBC and Credit Suisse declined to comment, while Goldman Sachs was not available for comment.