GUARANTY DATED AUGUST 12, 2003 BETWEEN FIRST ENERGY CORP. AND ATLAS RESOURCES, INC. TO GAS PURCHASE AGREEMENT DATED MARCH 31, 1999 BETWEEN NORTHEAST OHIO GAS MARKETING, INC., AND ATLAS ENERGY GROUP, INC., ATLAS RESOURCES, INC., AND RESOURCE ENERGY, INC.

Exhibit 10(f)

GUARANTY DATED AUGUST 12, 2003

BETWEEN FIRST ENERGY CORP. AND ATLAS RESOURCES, INC.

TO GAS PURCHASE AGREEMENT DATED MARCH 31, 0000

XXXXXXX XXXXXXXXX XXXX GAS MARKETING, INC., AND ATLAS ENERGY GROUP, INC., ATLAS RESOURCES, INC., AND RESOURCE ENERGY, INC.