I have driven in most of Europe including Slovenia, Croatia and Greece this year but would like some imput before renting a car and driving in Romania and Bulgaria.
I last visited Bulgaria in 2001, so things may have changed since then. But, here's what I recall. Besides a stretch of highway between Sofia and Plovdiv, Bulgaria has virtually no freeways. Expect much longer driving times here. The government maintains the roads in decent, if not ideal, conditions. Most roads I experienced appeared safe enough. Petrol stations are not as plentiful as in the West (or even in the neighboring former Yugoslav nations), but numerous enough that you should never run out of fuel. One thing that is not abundant: road-side rest stations! You may have to get a little creative if nature calls.