READ COMMITTE without START TRANSACTION?

Hello,

I need to run some SELECT queries that take a while (10+ minutes) to complete, and I'm wondering about the isolation about the results I get. More precisely, while my SELECT is running, the DB is being updated by another application, and I am wondering which, if any, data changes my SELECT will see.

Example:
If I start my SELECT at 10:00, and it finishes at 10:10, will my results include data that was inserted between 10:00 and 10:10?
Similarly, will my result include data that was updated between 10:00 and 10:10?
The same question for data that was deleted during that period.

If it matters, my SELECT runs from psql client, while concurrent inserts, updates, and deletes are executed from a separate application (webapp).

For my purposes in this case I need the SELECT to get the results that represent data right at the beginning of the query - a snapshot. I read this: http://www.postgresql.org/docs/8.1/static/transaction-iso.html and it looks like this is the default PG behaviour (READ COMMITTED)

Question:
If I do not explicitly START TRANSACTION before the SELECT, will this READ COMMITTED XA behaviour still be in effect?

Thanks,
Otis