Q: I am a tenant in a house I rented last summer, planning on staying a year, but soon after I moved in, the owner told me that he was having trouble making his mortgage payments. Last month, the bank foreclosed and I just got a 30-day notice. Unfortunately, I don't have a signed formal lease. Can they do this?

A: Let's begin with your statement that you don't have a "signed formal lease." Your regret as you report this suggests that you think it's a problem, but that's not necessarily so.

First, let's dispense with the term "formal." That word has no legal meaning. Either you have a lease (or rental agreement) or you don't. The question isn't whether you signed a lengthy document with appropriate pomp and circumstance, but simply whether you and the landlord reached a true agreement when you struck the deal.

As long as you had a "meeting of the minds," in which you both agreed to the key terms of the arrangement, you had a contract. That you didn't reduce it to writing in this context does not make it invalid.

An oral lease (for no more than a year) or an oral rental agreement (renting month to month, until one of you terminates) is perfectly legal. It's always better to put your arrangement in writing, but failing to do so doesn't make the underlying agreement invalid or unenforceable in court.

So the question really is, what did you and the landlord agree to? You were "planning on staying a year," but that doesn't necessarily tell us that you and the landlord agreed that you had a lease for a year. Instead, you might have agreed to rent month to month, hoping that you'd be happy and would stay on for a year.

You can probably already see why it's always a good idea to write down the terms of the deal and have everyone sign it: As long as the written agreement is clear, there will be no problem figuring out the terms, including how long the arrangement was supposed to last and how it could be terminated. With an oral agreement, you're at the mercy of each other's memories (and possible biases).

Now let's get to the nub of your question: Could you be tossed out by a new owner on 30 days' notice, following foreclosure? That depends on who bought the property, and for what reason:

If you had a lease, and the new owner bought directly from the foreclosing party (the bank or lender), and is a natural person who intends to live in the house as his or her primary residence, that person can terminate, but must give you 90 days.

If you had a lease and the purchaser is a corporation, real estate investment trust or other legal entity, or an actual person who will use it other than as a primary residence (as a rental, for example), you are entitled to stay for the length of your lease, just as you would if the home had been sold in a regular sale to a new owner.

If you had a monthly rental agreement, however, your agreement can be terminated on 90 days' notice, no matter who buys at the sale. Still, that's better than 30 days.

If you believe that you and the prior owner had a lease, you'll need the prior owner's cooperation to bolster your claim to the new owner (and possibly to a court, if you refuse to move and trigger an eviction) that you're entitled to the protections for lease-holding tenants. Without a written document, you'll want at least a sworn declaration from the prior owner, stating that your oral agreement was intended to be a lease. Hopefully, the new owner will believe the two of you.