* Retail investors can sign up online or at local banks
* Retail will be sold up to 0.5% of state oil giant
* Marketing blitz includes endorsement by clerics (Recasts, adds Alinma Bank CEO, local investor comments)
By Marwa Rashad and Stephen Kalin
RIYADH, Nov 17 (Reuters) - From taxi drivers to clerics, Saudis clamouring to own part of state oil giant Aramco went online and to local banks on Sunday at the start of a long-delayed share sale for what could be the world's biggest initial public offering.
Ahmed Sanad, 37, who signed up at a Saudi British Bank (SABB) branch in central Riyadh called the IPO, which has dominated conversations on social media, in cafes and at family gatherings, "the talk of the town" and "a global event".
"I don’t think anyone will miss the opportunity. There are no better options at the current time," he told Reuters as banks extended working hours to meet high expected demand during a sale process that runs until Nov. 28.
Roadside billboards and shopping mall adverts hailing "Saudi Aramco, soon on Tadawul", have for weeks been trailing the listing of the world's most profitable company through a listing on Riyadh's Tadawul bourse.
Retail investors will be able to buy up to 0.5%, about $8.5 billion worth of shares, in the Aramco IPO, valuing the company at $1.6 trillion to $1.7 trillion.
Aramco's high-profile advertising campaign contrasts with another bumper share sale this month, the secondary listing of Chinese retailer Alibaba, which is pursuing Hong Kong's first paperless listing.
In the Aramco IPO, retail investors are entitled to one bonus share for every 10 they buy if they hold on to their stock for 180 days. Saudi media have reported that up to 5 million people are expected to participate in the domestic flotation.
Abdullah al-Faqeeh, a 29-year-old dentist, began saving to buy Aramco shares once de facto Saudi ruler Crown Prince Mohammed bin Salman announced the plans nearly four years ago.
"I will get bonus shares, and with the profits I will buy more shares. It is a once-in-a-lifetime opportunity," he said.
Saudi banks are marketing loans, with some offering four times the usual limits, two financial sources told Reuters, adding that they are able to do so as they will hold the stock on behalf of clients so have it as security.
Abdulmohsen al-Fares, chief executive of Alinma Bank which operates according to Islamic law, told Reuters that clients could receive immediate approval for lending facilities.
"We are very optimistic there will be a lot of participation... We are expecting it will be overcovered."
Senior Muslim clerics, including royal court adviser Sheikh Abdullah al-Mutlaq, said investing in Aramco is permissible.
"It (Aramco) is a pillar of the Saudi economy," Mutlaq, a member of the kingdom's top clerical body, said in response to a caller's question on a weekly radio show on Friday.
"I think even the scholars, we will participate in it."
Aramco said on Sunday it plans to sell 1.5% of its shares or about 3 billion shares, at an indicative price range of 30 to 32 riyals, valuing the IPO at as much as 96 billion riyals ($25.6 billion) at the top end of the range. It could beat Alibaba's record $25 billion IPO in 2014.
The chairman of another Riyadh-listed firm said he and others in the business community were looking to invest: "It's the greatest quality by any standard. Best-in-class."
The government has pushed rich Saudis to invest, with many viewing it as an opportunity to show their patriotism after a September attack on Aramco facilities that struck at the heart of the kingdom's energy industry.
Washington and Riyadh blamed regional rival Iran for the attacks, which temporarily cut more than 5% of global oil supply. Tehran has denied any involvement.
"Participating in the Aramco IPO is a national duty for whoever can afford it," Saudi columnist Anwar Aboalela tweeted.
Thousands of Saudis are seeking to invest on behalf of their dependents, to increase the number of shares they can buy, two bankers told Reuters.
Saud al-Tukhaify, who signed up for himself, his wife and three children, called it an opportunity to "become partners" with Crown Prince Mohammed, who pushed to take Aramco public to help fund reforms aimed at weaning the economy off oil.
On Twitter, trending hashtags about the IPO included photos and praise for the 34-year-old prince.
Although some think he is wrong to relinquish even partial control of Aramco, the lure of holding shares is hard to resist.
"Aramco will be a winning horse," said Uber driver Abu Mohsen. "I will subscribe only because of the expected gains but I remain against the sale, especially to foreigners."
Additional reporting by Saeed Azhar in Dubai; Editing by Pravin Char and Alexander Smith