HI Scott,
Great idea for a theme and lots of potential here. I had fun thinking about this on my way home the other day. Here are some thoughts about problem areas of the current design and possibilities for refinement:
1. Gas prices: with the current pricing chart, the only way to make a profit is by buying gas on a six and selling it on a 1-3. Presumably, players will not start with enough gas and cash to get through the game without making some money along the way. As Chainyank suggests, this almost forces players to buy gas when they roll a six. Consider adjusting the pricing so there are more opportunities for (at least somewhat) profitable exchanges. Of course you'll need to make sure this doesn't feed into...
2. Gas Tycoons: total profit for any pair of gas transactions will be profit/gallon times the number of gallons sold. But profit also translates to increased gas stores, so successful traders' profit generating capabilities will increase geometrically, possibly leading to wildly disparate money generating capabilities between players. Consider placing limits on how much gas players can buy in a turn. Perhaps cars have a limited fuel capacity and you can't buy more than you can fit in the tank. Or have the number rolled represent the number of gallons that could be bought (or sold) on a turn instead of representing fluctuating market prices.
3. Toll Booths: these might be redundant. They clearly came over from Fictionless, where they provided a mechanism for players to need money. But in Petrol Panic, players already need money--to buy gas to get to the finish line, so the toll booths seem like a bit of an artificial construct to force players to engage in the monetary portion of the game. This could probably be done more organically by manipulating the gas market (and supplies!). Perhaps toll booths could be replaced by gas stations where gas is available relatively cheaply and in limitless, or at least large, quantities. You could have a scenario where players buy gas cheap at the stations, and try to sell it for a profit on the road, but still need to maintain their own supply to make it to the next gas station.
4. "Petrol Panic:" the name evokes visions of gas lines, skyrocketing prices and desperate drivers, but in the current design, the sources of tension are in speed/distance for the racing part, and/or raw money from the economic part (depending on the victory conditions you settle on). Consider making gas a limited commodity that will run out by the end of the game, preferably stranding one or more players short of the finish line. Perhaps each gas station would have only a limited supply--first come, first served, but of course there's no point getting there early if you haven't earned enough money to buy anything. You might even work out a way to get an auction mechanism in, at least for the last few precious gallons, and/or allow the players to buy and sell among themselves for whatever price they can agree on.
Other ideas to play around with:
Fuel efficiency: instead of making the top speed the most fuel efficient (three space/gallon), what if you made fuel efficiency decrease after a certain point (for example, have it cost three gallons to move six spaces). That way players could have to make a choice about whether they wanted to make full use of that six they just rolled for the speed, or slow it down a little bit to conserve fuel.
Different cars: Not all cars were created equal. It might be fun to have both gas guzzlers and more efficient cars competing in the same race.
