Commit problem with Oracle 7.3 + Delphi 2

I am using Delphi 2.0 and Oracle 7.3, via ODBC on win 95.

My transaction seem to close automatically when I use a TQuery
component.
I tried to use a TDatabase object and I called StartTransaction(), but,
when I execute a query, (The TQuery component is linked with the
TDatabase one),
the query completes and closes the transaction :
  In fact, if I check InTransaction, it returns true but
  if I try to run a second query it generates an exception saying that
there is
  no active transaction !

Can you help me ?