Help With A Query... Hard To Explain

Hi all!, i would really appriciate it if you could help me out. I have this complex query... in one table i have dates and costs associated that show when fuel was put into the system

such as:
1/1/2008 -- $200
1/20/2008 - $100
1/25/2008 - $150

I then have another table that has data when fuel was taken out of the system
such as:
1/2/2008 -- ($50)
1/3/2008 -- ($20)
1/4/2008 -- ($10)

what i need is a query that is able to show a running tab on the fuel tank and how much fuel is in it...

so for example if it could spit out a result such as
1/1/2008 -- $200
1/2/2008 -- $150
1/3/2008 -- $130
1/4/2008 -- $120

If this is convoluted i can upload a little database..

Thanks! (Here is the current query i am using but its not working right.

SELECT DatePart("yyyy",[purchase_Date]) AS AYear, DatePart("m",[Purchase_Date]) AS AMonth, DatePart("d",[Purchase_Date]) AS ADay, DSum("gallons_purchased","purchase_fuel_tbl","DatePart('d', [purchase_Date])<=" & [ADay] & " And DatePart('m',
[purchase_Date])<=" & [AMonth] & " And DatePart('yyyy',
[purchase_Date])<=" & [AYear] & "") AS RunTot, fuel_use_tbl.fuel_date, fuel_use_tbl.external_ID, fuel_use_tbl.gallons, [RunTot]-[fuel_use_tbl].[gallons] AS cur_Value
FROM (tank_tbl RIGHT JOIN purchase_fuel_tbl ON tank_tbl.tank_ID = purchase_fuel_tbl.tank_ID) LEFT JOIN fuel_use_tbl ON tank_tbl.tank_ID = fuel_use_tbl.tank_ID
GROUP BY DatePart("yyyy",[purchase_Date]), DatePart("m",[Purchase_Date]), DatePart("d",[Purchase_Date]), fuel_use_tbl.fuel_date, fuel_use_tbl.external_ID, fuel_use_tbl.gallons
ORDER BY DatePart("yyyy",[purchase_Date]), DatePart("m",[Purchase_Date]), DatePart("d",[Purchase_Date]);