This video from the movie, "The Yes Men", along with the planet Illium in Mass Effect 2 (with indentured servants) puts this question in my mind:

As you can see laid out in the video, if someone is a slave owner, they have to provide health care, food, clothing and shelter for their slave, or their "investment" would go to waste.  Done in a developed nation it can be costly.  Well, as observed by the American economy, and the push for "right to work" and increasing on-demand temporary labor, and no guarantees of individuals even remotely ever making enough money to provide things like healthcare or shelter (there are homeless people who do work as day laborers), the market seems to have optimized itself to do what customers need, without people having things that even a slave would have.  So, the question here is: Is slavery no longer an economically viable option?  The Yes Men video indicates, AT LEAST, it isn't economically viable to have slaves in developed nations.  Just curious if planet Illium, for example, would end up having indentured servants on it. 

By the way, I would suggest anyone who doesn't know what the Yes Men are about, to go do a bit of research on them, if what you see there generates strong opinions of them. 

Everyone think they're free but, we're all slaves to a money base economy. We're forced to be employeed.

http://www.notforsalecampaign.org/

http://gvnet.com/humantrafficking/Brazil.htm

Still 27 million people enslaved today. From people held captive on farms deep in the Brazilian jungle to sex trafficking all over the world.

The sex trade happens in most developed nations. Also in my own country

http://www.salvationarmy.ca/2009/09/22/not-for-sale-victims-of-sex-trafficking/

It's easier and much faster for companies to just cut someone a check than cloth,house,medicate and feed them and their kids. If they made large apartment complexes, bought laundry machines, group health insurance plans and basic food at wholesale prices, wouldn't it wind up costing them more (on average)? I remember hearing somewhere that the cost to house a prisoner rivaled minimum wage.

Therefore you must outsource the taking care of slaves to a big slave company. The free market will drop the prices of employing slaves.

It is definetly a economically viable option.

So even if you have to provide all these things like food shelter and say healthcare it would still be a win.

Lets say you have slave males. Then just give them a dangerous job which earns more money like soldier or working on a oil rig. Or something like that. Provide food ? A 100 pound rice sack and 1 package of vitamine pills and some 2 pounds  butter every 3 months would be enough to keep someone healthy. And the price is very affordable. 2 pounds butter = 5 Dollar 100 pound rice= 100 Dollar 1 package vitamine pills 6 dollar = 111 Dollar/3 about 40 Dollar a month for food including water which is very cheap if you collect rain water or use tap water. electricity is not required for them also you could fit easily 10 in a garage or more in a basement.

Next thing shelter: Let them sleep in the garage or in the basement on a matress. Healthcare ? Why is that ? Slaves certainly dont need dental health care or treatment for minor maladies. And if they get really sick you just make a calculation if the numbers doesnt add up you just execute the slave. 

A slave would cost you 100 Dollars or less per month if you have a flat just let him sleep on the street and take all his money away except the 100 Dollar per month he needs to buy his rice.

And a slave could bring you in 2000 Dollars a month atleast if he has two jobs maybe more if he takes 3.

You just have to wash his clothes every week so the slave can be seen in todays society.

Or you buy just female slaves and sell them on the street. They bring you all the money they dont need to survive and thats it also they dont need shelter since they can sleep in a cheap motel with a client. Works also with young pretty male slaves.

what I described above is what a slave is. IT has no human rights and just needs to be alive for aslong as you have the purchase costs in plus some profit.A slave IS always an economically viable option ESPECIALLY IN THE WEST. Because in other places people can keep barely themselfs alive with their sallary. But in the west they have money for mobiles videogames flat meat electricity soft drinks clothing all goods which are not needed to survive so a slave earns significantly more then he needs to survive and thats making him always a good investment.

Would slavery be allowed we would have very fast a multi billion dollar industry and people in the west would be getting rich as hell because there are way more people on this planet then centuries ago also there would be no loss of "product" if you transport them. So prices for slaves would be cheap and people would buy instead of a new car 6-10 slaves which would work for them and help them to have a better life.

Rivaled minimum wage?  I would wager its a lot higher than that.  Minimum wage working the whole year is like $15k approximately.  These prisoners are being fed, and have guards all over the place, not to mention the judicial system going through their cases all of the time.

Human trafficking, which involves slavery of both the sexual and non-sexual type, is perhaps the most profitable criminal venture to engage in, explosive in growth opportunity, all the more so because a lot of countries look the other way on it more than on drugs or arms-smuggling or what have you.

The cost to keep people alive and healthy enough to give you a return is lower than you might think, especially since in the case of prostitutes you can just have your girls "arrested," then the state foots the bill for fixing whatever medical problems they might have, if minor enough to fix, then you get around to bailing them out

There is no question of viability

EDIT: Ninja'd by Netyaroze who gave the answer more comprehensively, but yeah.

But never forget, that slaves don't have wages, so Industrial/Comercial/Information (whatever the name now) would crumble and die without payed labours.

Slaves are extracted from the bottom rungs of society financially. Their lost potential contribution as income earners are generally not missed, especially in the cases of poor farm families in some countries that sell their kids off for more than those kids could have made in a year