You may be shocked to find that petrol is even more expensive than in England (it is one of the main ways that the Turkish Government raise tax revenues). However, having a car for your holiday is well worthwhile, and enables you to do far more exploring, both locally and at greater distances, than you would otherwise manage – as well as allowing you to choose your routes and timings to suit you.
Driving in Turkey is not as horrific as some guidebooks would have you believe. The roads are relatively traffic free, and there is nearly always an overtaking lane to use (depending on which lane is travelling uphill at the time). Most road signs are fairly obvious, and even the extensive road improvement schemes rarely cause any significant delay. Do though be aware that because of the amount of up and down and around bits (other than along the coast road, most journeys are inland and hence ‘over the mountains’) most journeys will take longer than you anticipate based solely on distance. You probably won’t average much more than about 75km per hour.
Be aware that when you are driving, you should always carry both your driving licence and your passport. There are frequent random police stops, please slow down for these, occasionally they will ask you to stop, and have a quick glance in the car before waving you on.
In most major towns, there will be several different types of car park. These range from British style multi-stories (which may even include your first hour free if you spend a certain amount at the associated supermarket), through to patches of almost waste land. These operate on the principle of cramming as many cars in as possible, hence you leave the keys with the attendant. This type is particularly common in towns such as Marmaris or Bodrum.
There are many roadside services, ranging from European style petrol stations, (most of which take credit cards) through to little ‘shacks’ that sell most of the usual refreshments, obviously cash only. If you are travelling somewhere, a Village Breakfast ('köy kahvaltı') is highly recommended, amazing food and service even at the most decrepit looking cafes. There are petrol stations every few kilometres on most of the major roads.
And of course look out for the stuffed sheep sellers – laybys full of stuffed sheep, which no one ever seems to buy, and which no Turk has ever been able to explain.