most economical car to run?

tips can be given but depend on amoount you wish to spend
I say this because with some of the newer engines there are tax advantages so it is not just the fuel but car tax,insurance,depreciation etc

I'm getting 62.2 mpg from my diesel Yaris & Road Tax is £35 p.a.
Add to this the excellent reliability & life expectancy of the car ( & resale value) & you've got a winner.

I think depreciation is a big problem, some cars seem to lose so much at the start of their life. I tend to go for cars that are 3-4 years old. I've never had a brand new car and don't think I would buy one.
I think diesels are good for economy and there are some journeys where you could bicycle rather than take the car when you nip out for a paper.

And it's not just the car, if you have an inexpensive honest garage that will make any cars running costs more economical.

It's all well and good to say "I get xx mpg" but you are limiting your ability to compare against all modes of transport. It would be far better if everyone was able to get used to converting their mpg into pence per mile (ppm) or £per 100 miles

I say this because I used to drive an Vauxhall Omega 2.0 Estate on LPG and I could drive 700 miles on £28 - non stop - If I had a full tank of petrol that would take me a further 400 miles (this was when petrol was 82p-87p litre).
= 0.04 (or 4p per mile) £4.00 per 100 miles
Using the price of 82p per litre and the best mpg so far in this thread (65mpg) 65mpg = 0.057 or 5.7pence per mile £5.70 per 100 miles

Using current petrol prices £1 per litre 65mpg = 7 ppm £7 per 100 miles.
I have no idea what price I could buy LPG at today so I can't give an updated figure for LPG

So you can see that my LPG car was nearly 30% cheaper to run than the best petrol or diesel car. But it is heavily dependant on the price you can source LPG for locally. The price of LPG varies a lot more than the price of petrol/diesel does.

Apparently a Polo bluemotion is pretty good - but I don't have the figures.
Also a diesel Smart fortwo but they are not available in UK excep as imports and you would have to be able to get along with a very small car.