My 3000+ sq ft (incl basement) house has two-zone heating/cooling, with an
oil furnace and air conditioner for the basement and first floor, and a heat
pump for the upstairs.

I bought the house three years ago, when oil was less than $2.00 per gallon.

Due to the high cost of oil, I called the oil company about budget billing
(same price every month), and was told they are using $4.50 per gallon as a
planning number for next heating season, and said I use about 280 gallons
per heating season.

Also, I live in Maryland where the local utility company was deregulated and
for the first time in 15 years, was able to raise rates last year. They
claimed it was a 50% increase. I don't see how a jump from about $150 to
$300 per month is 50%. That's 100%. With oil heat on the first floor, my
annual monthly average use is about 2400 kWh per month.

Where I live there is no natural gas available.

I'm sure this has been discussed here before, but is it worth an investment
for me to switch from oil and a/c for the basement and first floor to a
second heat pump or other energy source? If so, what other factors need to
be considered, for example will my electric panel be able to handle two heat
pumps? I have neighbors with two heat pumps rather than one plus oil/ a/c -
that's what the builder installed for them.

What about a propane tank?

Finally, my oil tank is full. Would I be better to deplete it over the next
winter, then convert?

What is a typical cost to convert? Will a HVAC company dispose of the oil
tank? Any other issues to consider? If this is a viable investment, how
long will it take to realize a positive return on the investment?