What is the LONGEST Tour operated by travel companies?

This one kinda straddles the line between accommodation and travel, but I believe it still qualifies.

There are several cruise ships that offer the public a chance to lease a cabin for an extended period of time (in some cases up to 60 years) and live there full time if you so choose. These vessels are called residential yachts. You can live (and sometimes work) on board the ship as it travels round the world. The destinations are usually voted on by the residents.

These leases can be quite expensive and also come with a monthly fee to cover cost of living, maintenance and upkeep of the ship.

A notable example was the MS The World (wiki), launched in 2003. Currently all of its cabins are owned, but there are several other residential yachts that (as of 2020) have available cabins.

Two such ships (as of Mar 2020) are :

• StoryLines
• Utopia

These aren’t cheap, but i think you’ll struggle to find a longer tour than a 60 year lease on one of these vessels.

Viking offers a 245-day round-the-world cruise, which starts (and ends) in London. It visits 53 countries on six continents.

MadVenture Travel is now offering:

LONDON TO SYDNEY OVERLAND (via Africa & central Asian silk road)

which promises to be a 64 week, 61 country odyssey!!

From their site:

A 64 week in-depth overland expedition from London to Sydney
travelling through Africa, the Middle East, central Asia and
Australasia visiting highlights and natural wonders of 61 countries
including UK, France, Spain, Morocco, Western Sahara, Mauritania,
Senegal, Gambia, Guinea Bissau, Guinea, Sierra Leone, Liberia, Ivory
Coast, Ghana, Togo, Benin, Nigeria, Cameroon, Equatorial Guinea,
Gabon, Congo, Democratic Republic of Congo, Angola, Namibia, Botswana,
South Africa, Lesotho, Swaziland, Mozambique, Zimbabwe, Zambia,
Malawi, Tanzania, Rwanda, Uganda, Kenya, Ethiopia, Sudan, Egypt,
Jordan, Syria, Lebanon, Turkey, Georgia, Armenia, Azerbaijan,
Turkmenistan, Uzbekistan, Tajikistan, Kyrgyzstan, Kazakhstan, Russia,
Mongolia, China, Laos, Vietnam, Cambodia, Thailand, Malaysia,
Singapore, Indonesia and Australia.

A two-year tour of World Heritage sites (962 places) is now available, offered by a British luxury company. By the way, it costs about 1 million pounds. It claims to cover all the sites if they are safely accessible.

The Daily Mail lists some of the stops.

One day, while travelling online with google maps, I zoomed onto Ushuaia and got caught by a ship named Peace Boat.

This ship takes passengers for cruises around the world that last about 100 days.

EDIT, Nov,2016: Google Maps has updated its satellite imagery. Peace Boat is no longer visible.

UKTOOZ appears to offer a 28 Week London to Sydney trip

http://uktooz.com/

A 28 week in-depth overland expedition from London to Sydney visiting the highlights and natural wonders of over 23 countries including Turkey, Iran, Pakistan, India, Nepal, Tibet, China, Laos, Vietnam, Cambodia, Thailand, Malaysia, Singapore, Indonesia and Australia!

G Adventures still has an 82 day trip.

Would going on a cargo ship count as a tour? In that case there is a tour operator offering various tours, of which their offers on oceania, are quite long. One example being

Rotterdam-Dunkerque-Le Havre-New
York-Savannah-Kingston-Manzanillo-Panama
Canal-Papeete-Laukota-Noumea-Brisbane-Sydney-Melbourne-Tauranga-Napier-Panama
Canal-Manzanillo-Savannah-Philadelphia-Tilbury-Rotterdam, duration ca.
84 days

Especially since they offer intermediate stops, you can prolong this “tour” for quite some time

Since we don’t really care about the mode of transportation:

143 nights: http://www.rssc.com/cruises/VOY121024H/Itinerary.aspx

115 nights: Silver Sea World Cruise

115 nights: Holland America World

At one point there was a 335 night cruise but as far as I can tell that company is now out of business 2010.

Had to add this

Around the world by Freighters:

125 days starting from Houston

This Russian company offers a world-wide cruise for the 140 days, from New Zealand to Norway (being honest, there are no countries from both Americas :).

There are over 100 cities in 31 countries being visited during this cruise.

Places are from $77,270 to $261,070 per person, trip is being made on Seven Seas Voyager.

I think search for another world-wide tours by ship is very perspective.

Ozbus offer a 29 week tour of South America, starting and finishing in Quito.

http://www.oz-bus.com/oz-bus-south-america/oz-bus-south-america.aspx

Update:
Ozbus have sadly ceased trading as of april 2012

Sydney – London by bus was the longest i could think of, but it’s only 92 days and crosses 18 countries.