Irvine-based Opus Bank has agreed to acquire 10 banking offices in Southern California from Los Angeles-based PacWest Bancorp, a buy that would bring a total of about $145 million in deposits to Opus.

Opus is set to pay a 2.5% “blended deposit premium” for the deposits, according to the bank.

The 10 branches of PacWest’s subsidiary Pacific Western Bank are spread over Los Angeles, San Diego, San Bernardino and Riverside counties.

Opus Chief Executive Stephen Gordon said the acquisition will complement Opus’ “existing 23 banking offices in Los Angeles, Orange, and San Diego Counties, while additionally creating Opus Bank’s initial presence in Riverside and San Bernardino Counties.”

Opus is the largest bank based in Orange County based on assets, with about $2.4 billion.

PacWest has $5.4 billion in assets and is in the process of acquiring San Luis Obispo-based American Perspective Bank for $58.1 million.

The deal will give Opus four new banking offices in Los Angeles County: in Encino, Westwood, Monrovia and South Pasadena. It also will get branches in Carlsbad, El Cajon and La Mesa in San Diego. The other newly acquired offices will mark a debut for Opus in the Inland Empire, with offices in Chino and Twentynine Palms in San Bernardino County, and La Quinta in Riverside County.

Pacific Western will operate 66 offices throughout California after the deal, which is expected to close by the end of this year.