Can't quote in US MPG figures but I can quote in litres/100km (or even MPG imperial which we stopped using here in Australia 30 years ago).

Our 1990 300TE (M103 with 4 speed auto) with more weight and shorter final drive gearing than 300E or 300CE regularly returns 10 litres/100km (28 mpg) on the highway (at not much over our strictly enforced 100km/h and 110km/h limits) with family and luggage on board.

My father's 1993 E320 coupe (M104 with 5 speed auto) returns around 9 litres/100km (31.5 mpg) under the same conditions with 2 adults and luggage.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.