(7) A closing agreement, as the term is used herein, is an agreement between the Commissioner of Internal Revenue or his delegate and a taxpayer with respect to a specific issue or issues entered into pursuant to the authority contained in section 7121 of the Internal Revenue Code. Such a closing agreement is based on a ruling which has been signed by the Commissioner or his delegate and in which it is indicated that a closing agreement will be entered into on the basis of the holding of the ruling letter. Closing agreements are final and conclusive except upon a showing of fraud, malfeasance, or misrepresentation of material fact. They may be entered into where it is advantageous to have the matter permanently and conclusively closed, or where a taxpayer can show good and sufficient reasons for an agreement and the Government will sustain no disadvantage by its consummation. In appropriate cases, taxpayers may be required to enter into a closing agreement as a condition to the issuance of a ruling. Where in a single case, closing agreements are requested on behalf of each of a number of taxpayers, such agreements are not entered into if the number of such taxpayers exceed 25. However, in a case where the issue and holding are identical as to all of the taxpayers and the number of taxpayers is in excess of 25, a Mass Closing Agreement will be entered into with the taxpayer who is authorized by the others to represent the entire group. See, for example, Rev. Proc. 78-15, 1978-2 C.B. 488, and Rev. Proc. 78-16, 1978-2 C.B. 489.