A wine cellar needs checking but an oil cellar does not.

Question: What is the difference?

Answer: The quantity of oil is fixed (for any given meal) but the quantity of wine is not [so the servant will often need to go to the cellar during the meal to bring more wine and will have bread in his hand].

Neither a wine storeroom nor an oil storeroom require checking.

Question: When is it considered a wine cellar [rather than a storeroom]?

Answer: If it is located in the courtyard adjacent to the room in which one puts bread (Pnei Moshe)

There is a cellar that is considered a storeroom and there is a storeroom that is considered a cellar -

A cellar in which one is embarrassed to eat is considered a storeroom.

A storeroom in which one is not embarrassed to eat is considered a cellar.

There is a courtyard that is considered an alley and there is an alley that is considered a courtyard -

A courtyard that many pass through is considered an alley (and it does not require checking).

An alley that many do not pass through is considered a courtyard (and it requires checking).

Question: But perhaps the donkey drivers brought bread into the storeroom when coming to taste the wine (so why is a storeroom exempt from being checked)?

Answer: They only bring in sweet fruits, not bread (this assists them in tasting the wine before they purchase it).

(Beraisa): One who departs on a voyage -

If it is more than 30 days before Pesach, he is not required to check.

If it is less than 30 days before Pesach, he is required to check.

This only applies to one who plans on returning before Pesach, but if not, even if it is more than 30 days before Pesach, he is still required to check.

This exemption from checking if it more than 30 days with intent to return is only when he is unsure if he has Chametz in his house, but if he is certain that he has Chametz there, he must return even if he leaves at the beginning of the year.

Rebbi Abba: Even if he intends to return he must still check, lest he decide not to return.