In a separate statement, flyadeal said it will operate an all-A320 fleet.
Last month IAG said it meant to buy 200 Boeing 737 Max aircraft.
"This order will end in flyadeal working an all-Airbus A320 fleet sooner or later", it mentioned.
Flyadeal said the allocation of the new aircraft came after an agreement for a total of 100 aircraft which Saudi Arabian Airlines Corporation (SAUDIA) signed during the Paris Air Show in June this year.
Earlier this year, Indonesian airline Garuda canceled a multibillion-dollar order for 737 Max 8 jets.
The 737 MAX stays grounded worldwide, and regulators should approve the fix, and new pilot training earlier than the jets can fly once more. "Airbus needs to find ways to increase its production capacity for its A320 line of aircraft, which isn't easy to do". Meanwhile, Emirati carrier flydubai said in April it could order A320neos as replacements for the MAX jets.
The Max was grounded globally after the Ethiopian crash and there is still no firm timetable for returning the planes to service.
The airline's network is now limited to eight domestic Saudi Arabian destinations, which it hopes to expand to 24 in the near future. Preliminary investigations point to the role played by new software on the jet. The list price for the 20 Max 737s, each of which costs about $117 million, would normally run $5.9 billion, though Flyadeal would have gotten an undisclosed discount. Lawyers for victims' families were dismissive of the move.