(Bloomberg) —Saudi Arabia is preparing contingency plans for a possible delay to the initial public offering of its state-owned oil company by a few months into 2019, according to people familiar with the matter.

While the government is still aiming for a Saudi Aramco IPO in the second half of next year, that timetable is increasingly tight for what’s likely to be the biggest share sale in history, the people said, asking not to be named discussing internal deliberations.

Saudi Aramco said in statement the IPO “remains on track. The IPO process is well underway and Saudi Aramco remains focused on ensuring that all IPO related work is completed to the very highest standards on time. It didn’t give a timeframe. The comment was echoed by a Saudi government source Wednesday. Officials have previously said the most likely schedule is the second half of next year.

Several important decisions on the IPO have yet to be taken, stretching the ability of the company and its advisers to sell shares before the end of next year.

For example, Saudi Arabia has yet to announce where it will sell shares in Aramco other than the domestic stock exchange in Riyadh. The country may not to make an announcement until late October, when it’s holding a big investment conference in Riyadh. The delay in selecting a foreign exchange, mostly likely London or New York, has had a knock-on effect on other preparatory work.

Aramco Valuation

Saudi Arabia is also contending with weaker oil prices, which will help determine the value of Saudi Arabian Oil Co., as Aramco is formally known. The government has previously said the valuation may reach $2 trillion, while analysts, including those at Sanford C. Bernstein & Co. and Rystad Energy AS, have tended to give lower estimates.

Riyadh built a coalition between OPEC and other oil producers last year to reduce supply and bolster prices that by then had already retreated for two consecutive years. The oil glut has yet to dissipate and analyst forecasts compiled by Bloomberg show prices won’t average $60 again until 2019. Brent crude on Thursday was trading down 0.3 percent at $54.99 a barrel as of 8:04 a.m. in Singapore.

Should Saudi Arabia achieve its valuation of $2 trillion, the 5 percent stake it plans to sell would raise about $100 billion. That would eclipse the $25 billion raised by Alibaba Group Holding Ltd. in 2014, the current record.

Aramco Chief Executive Officer Amin Nasser said in January that the IPO was most likely to take place in the second half of 2018. Previously, Saudi officials said a flotation was planned for some point in 2018.

The share sale is the cornerstone of Vision 2030, a much wider plan conceived by Crown Prince Mohammed bin Salman to reshape the Saudi economy and diminish its dependence on oil.

Saudi Aramco has hired JPMorgan Chase & Co., Morgan Stanley, HSBC Bank Plc, Moelis & Co. and Evercore Partners Inc. to advise on the IPO. Independent Wall Street consultant Michael Klein is advising the oil ministry.