(Delta.com)

Delta Airline's new fare class, called Basic Economy, is basic indeed.

The new fare offers the airline's lowest prices but even more restrictions than the already restricted non-refundable economy-class fares offered by airlines and purchased by most leisure travelers. In essence, you purchase the fare itself - but nothing else.

Most significantly, there are no advance seat assignments. Considering Delta's load factor was 84 percent in March 2012, up from roughly 80 percent a year earlier, this means you better not mind sitting in a middle seat if you choose Basic Economy because there's a good chance that's what you'll get.

Second, there are no reservation changes. Period.  On most non-refundable tickets, travelers are able to change a ticket for a fee, usually about $150. Not with Basic Economy.

"It's a good option for the most cost-conscious customers," Paul Skrbec, Delta spokesperson, told ABCNews.com.

On Delta's web site, Basic Economy is shown as fare class "E." There is a separate column for Basic Economy and on a search for the fare on a flight from  Detroit to Orlando on Delta.com, the fare was clearly marked and it was obvious what I was about to purchase. However, for people who don't buy airline tickets on a carrier's web site, there's potential for confusion. A search for the same flight  on Expedia showed the lowest Basic Economy fare and indicated it was "E" class, but unlike the Delta website, gave no explanation of what that meant.

In my test search, the price difference between Basic Economy and Economy was $15. The airline said the price difference would fluctuate depending on market, route and seasonality.

With no option to secure a seat assignment and no changes allowed, there's good reason to pause before clicking the purchase button. But the airline points out that these fares do qualify for Delta Sky Miles, good news for airline loyalists. Customers earn regular  mileage as well medallion qualifying miles for elite status. In addition, medallion customers who purchase these fares are still entitled to the usual perks, like free upgrades on domestic flights.

For now, the new fare class is only available on flights between Detroit and Orlando, Tampa, Fort Myers and Fort Lauderdale, Fla. Will Basic Economy be introduced on other routes in the future?  Paul Skrbec, Delta spokesperson, told ABCNews.com the airline is "looking at it's [Basic Economy's]  performance and customer response. "