<PAGE>   1
                                                                    EXHIBIT 12-1

 MCN ENERGY GROUP INC.  AND SUBSIDIARIES
 COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES

 (DOLLARS IN THOUSANDS)

<TABLE>
<CAPTION>

                                           TWELVE MONTHS    TWELVE MONTHS     TWELVE MONTHS      TWELVE MONTHS      TWELVE MONTHS
                                              ENDED             ENDED             ENDED              ENDED               ENDED
                                        DECEMBER 31, 1998 DECEMBER 31, 1997  DECEMBER 31, 1996  DECEMBER 31, 1995   DECEMBER 31,1994
                                           (Restated)*       (Restated)*
                                        ----------------- -----------------  -----------------  -----------------   ----------------
<S>                                        <C>                <C>               <C>                 <C>                <C>
EARNINGS AS DEFINED (1) (5) (7)
Pre-tax income (2) (6)                     $ (63,904)         $ 145,441         $ 142,229           $ 124,583          $  95,888
Fixed charges (3)                            107,010             87,017            71,698              56,313             49,118
                                           ---------          ---------         ---------           ---------          ---------

     Earnings (loss) as defined            $  43,106          $ 232,458         $ 213,927           $ 180,896          $ 145,006
                                           =========          =========         =========           =========          =========

FIXED CHARGES AS DEFINED (1) (4) (5) (7)
Interest, expensed                         $  79,449          $  64,981         $  56,963           $  46,357          $  43,582
Interest, capitalized                         10,832              5,709             6,413               2,710              2,928
Amortization of debt discounts, premium
     and expense                               2,869              2,357             2,173               1,626              1,325
Interest implicit in rentals                   2,380              2,058             2,312               2,262              1,959
Preferred securities dividend requirements
     of subsidiaries                          17,613             14,433             5,001               4,424              1,413
                                           ---------          ---------         ---------           ---------          ---------

     Fixed charges as defined              $ 113,143          $  89,538         $  72,862           $  57,379          $  51,207
                                           =========          =========         =========           =========          =========

Ratio of Earnings to Fixed Charges                                 2.60              2.94                3.15               2.83
                                                              =========         =========           =========          =========

Coverage Deficiency (8)                    $  70,037
                                           =========
</TABLE>

*Certain amounts have been restated primarily to record cost of gas expense,
including trading losses, in the appropriate accounting periods as described in
Note 1b to the Consolidated Financial Statements.


(1)  Earnings and fixed charges are defined and computed in accordance with Item
     503 of Regulation S-K.

(2)  This amount represents the aggregate of (a) the pre-tax income from
     continuing operations of MCN and its majority-owned subsidiaries, (b) MCN's
     share of pre-tax income of its 50% owned companies, and (c) any income
     actually received from less than 50% owned companies.

(3)  Fixed charges added to earnings are adjusted to exclude interest
     capitalized during the period for nonutility companies and the preferred
     securities dividend requirements of MichCon included in fixed charges but
     not deducted in the determination of pre-tax income.

(4)  Fixed charges represent (a) interest, whether expensed or capitalized, (b)
     amortization of debt discount, premium and expense, (c) an estimate of
     interest implicit in rentals, and (d) preferred securities dividend
     requirements of subsidiaries, increased to reflect the pre-tax earnings
     requirement for MichCon.

(5)  In June 1996, MCN completed the sale of The Genix Group, its computer
     operations subsidiary. For purposes of calculating the Ratio of Earnings to
     Fixed Charges, it has been classified as a discontinued operation and
     therefore excluded from the ratio for all periods presented.

(6)  In 1998, MCN recorded several unusual charges, consisting of property
     write-downs, investment loss and restructuring charges, totaling
     $183,841,000 pre-tax ($114,576,000 net of taxes and minority interest).

(7)  MCN has decided to sell its E&P properties and accordingly has classified
     this segment as a discontinued operation. Therefore, for purposes of
     calculating the Ratio of Earnings to Fixed Charges, E&P is excluded from
     the ratio for all periods presented.

(8)  Earnings for the twelve-month period ended December 31, 1998, were not
     adequate to cover fixed charges. The amount of the coverage deficiency was
     $70,037,000. The Ratio of Earnings to Fix Charges for 1998, excluding
     unusual charges would have been 2.01.