AMENDMENT AND JOINDER TO OMNIBUS AGREEMENT DATED DECEMBER 18, 2006, AMONG ATLAS PIPELINE PARTNERS, L.P. AND ATLAS PIPELINE OPERATING PARTNERSHIP, L.P., ATLAS AMERICA, INC., RESOURCE ENERGY, LLC, VIKING RESOURCES, LLC, ATLAS ENERGY RESOURCES, LLC, AND...

Exhibit 10(u)

AMENDMENT AND JOINDER TO OMNIBUS AGREEMENT DATED

DECEMBER 18, 2006, AMONG ATLAS PIPELINE PARTNERS, L.P. AND

ATLAS PIPELINE OPERATING PARTNERSHIP, L.P., ATLAS

AMERICA, INC., RESOURCE ENERGY, LLC, VIKING RESOURCES, LLC,

ATLAS ENERGY RESOURCES, LLC, AND ATLAS ENERGY

OPERATING COMPANY, LLC