[Savoy]

Вот выдрал из английского Audi A4 Owner's Manual 2009 (стр. 251):

The correct grade of petrol is listed inside the fuel tank
flap. В моем случае это 98-й (95 min.).

The vehicle is equipped with a catalytic converter and must only be
run on unleaded petrol. Unleaded petrol must comply with the
European EN 228 standard. The petrol grades have different octane
ratings (RON). If, in exceptional circumstances, the correct octane
rating is not available, please note the following:

• For engines which require Premium unleaded petrol (95 RON)
according to ⇒ page 323, “Performance, weights and dimensions”:
Regular unleaded fuel with 91 RON can also be used. This will,
however, result in a slight loss of power.

• For engines which require Super Plus unleaded petrol (98 RON)
according to ⇒ page 323, “Performance, weights and dimensions”:
Premium unleaded fuel with 95 RON can also be used. This can,
however, result in a slight loss of power under certain driving conditions.
– If premium unleaded petrol is not available, the engine can
be run on regular unleaded petrol with 91 RON as an emergency
measure. In this case only use moderate engine speeds and a light
throttle. Fill up with premium or Super Plus petrol as soon as
possible.

Но на стр. 323 находим (ни слова про 98-й!):

Petrol engines
A4 1.8 Power output 118 kW at 4500 - 6000 rpm

Fuel Premium unleaded 95 RON or regular unleaded 91 RON *) В русской книжке такой информации вообще нет.

*) With slight loss of power

P.S. Спросил у дилера, какой лить 98-й или 95-й. Дилер сказал - 98-й лучше.