Standard & Poor's will put

Commerce Bancorp

(CBH) - Get Report

in the

S&P 500

after the close of trading Monday, replacing

Engelhard

(EC) - Get Report

, which is being acquired.

Commerce was gaining $1.17, or 3%, to $40.46. Standard & Poor's said after the close Wednesday that it would make the change in its most widely followed index.

When companies are added to an index like the S&P 500, their shares tend to rise because mutual funds whose composition tracks the index have to buy the stock.

S&P SmallCap 600 constituent

Reliance Steel & Aluminum

(RS) - Get Report

will fill Commerce Bancorp's spot in the S&P MidCap 400.

Stamps.com

(STMP) - Get Report

will replace Reliance in the S&P SmallCap 600.

Engelhard is being acquired by Germany's

BASF

( BF). Commerce Bancorp operates banks in New Jersey, Pennsylvania, Connecticut, Delaware, New York and other areas. The company is based in Cherry Hill, N.J.