RIYADH, May 13 (Reuters) - Saudi Aramco will sign on

Tuesday memoranda of understanding with U.S. liquefied natural

gas producer NextDecade ( NEXT ) and utility firm Sempra ( SRE )

, Aramco's chief executive said, as the oil giant expands

in the LNG market.

"The U.S. today, in terms of gas, is almost 100 billion

(dollars) in sales ... and it is continuously increasing,"

Aramco's CEO Amin Nasser told the U.S.-Saudi Investment Forum in

Riyadh.

"The U.S. is really a good place to put our investment," he

added, noting that under the MoUs Sempra and NextDecade ( NEXT ) would

supply around 6.2 million tons of LNG to Aramco.

The United States is already the world's largest exporter of

LNG and producers have plans in place that would double capacity

in coming years.

NextDecade ( NEXT ) last month signed a deal with a subsidiary of

Aramco, which is seeking to become a big player in the LNG

market, under which the U.S. firm will supply the superchilled

gas from its Rio Grande facility for 20 years.

"We do have other investments. So we're looking at, by 2030,

almost seven and a half million tons of LNG," Nasser noted,

speaking of expansion plans.

Nasser also said that one of the investments that Aramco

plans to sign on Tuesday involved an expansion of the Motiva

Port Arthur's refinery in the U.S., noting the oil giant would

invest $3.4 billion in the refinery.