Saudi state oil giant Aramco officially launched its initial public offering on Sunday, setting in motion what is expected to be the world’s largest ever share sale, even as questions remain over the company’s value.

After nearly four years of delays, Saudi Crown Prince Mohammed bin Salman gave the listing the go-ahead in recent days. The company hopes to first sell shares on the kingdom’s domestic exchange in December, or even before, and then attempt an international IPO.

The...