Adding Integers

The code below has this line
SET @SOGallons = @ODTGallons

I need it to add the Current value of @SOGallons to the newly selected value of @ODTGallons and set that as the new value of @SOGallons.

I've tried
SET @SOGallons = @SOGallons + @ODTGallons

SET @SOGalTemp = @SOGallons
SET @SOGallons= @SOGalTemp + @ODTGallons

Neither Worked

<CODE>
FROM [CSITSS].[dbo].[Orderdt] as ODT LEFT OUTER JOIN [CSITSS].[dbo].[Orddtcom] as OCOM
ON ODT.[Companydiv] = OCOM.[Companydiv] AND ODT.[OrderNumber] = OCOM.[OrderNumber] AND
ODT.[Sequence] = OCOM.[Sequence] WHERE ODT.[Companydiv]= 'GLPC-TRANS' AND ODT.[OrderNumber] = @OrdNum AND
([LineType] = 'IP' OR [LineType] = 'SO' OR [LineType] = 'DL' OR [LineType] = 'PU')

OPEN TC1

FETCH NEXT FROM TC1 INTO @LT, @ODTGallons, @ODTComm
WHILE @@FETCH_STATUS=0
BEGIN
IF @LT = 'SO'
BEGIN
SET @SplitTest = 1
SET @SOGallons = @ODTGallons
IF @SOGallons > 0
BEGIN
SET @SOGalTest = 1
END
ELSE
BEGIN
SET @SOGalTest = 0
END
IF @SplitTest <> @SOGalTest
BEGIN
SET @SOGalTest = 0
END
END
ELSE
BEGIN
SET @SOGalTest = 1
END
FETCH NEXT FROM TC1 INTO @LT, @ODTGallons, @ODTComm
END
CLOSE TC1
DEALLOCATE TC1</CODE>