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No, as far as we know an onward ticket is not required to enter Antarctica
Entry requirements for popular destinations
“This could include proof that you have enough money for your stay (at least 10,000 Thai baht per person or 20,000 Thai baht per family) and evidence of onward or return travel.”
100+ sold
“To get a VOA, your passport must meet Indonesia’s entry requirements, and you must have proof of your onward or return journey.”
10+ sold
“You must be able to show an onward or return ticket valid within the 90-day period.”
10+ sold
“Most UK visitors are also expected to have proof of return or onward travel.”
10+ sold
“Applicants must arrive on a carrier that is signatory to a Visa Waiver Program Agreement and at the time of arrival must have a round trip ticket that will transport the traveler out of the United States to any other foreign port or place as long as the trip does not terminate in contiguous territory or an adjacent island; except that the round trip ticket may transport the traveler to contiguous territory or an adjacent island, if the traveler is a resident of the country of destination.”
10+ sold
“show a return or onward ticket”
10+ sold
“Possess a valid return ticket to their home country or an onward ticket to a next destination country.”
10+ sold
“Eligible travelers may enter visa-free through any of the 65 open exit-entry ports and make cross-province visits in the permitted areas in the 24 provincial-level regions for no more than 240 hours, provided that they hold valid international travel documents and onward tickets with confirmed seats and departure dates.”
10+ sold
“You must have an onward or return ticket.”
10+ sold
“A confirmed return air/sea ticket or air/sea ticket and a visa for the next destination, and a confirmed seat reservation for departure flight.”
“you’re able to pay for your return or onward journey (or have funding from someone else to pay for the journey)”
“proof of a return or onward ticket”
“h. Carecer de boleto de retorno cuando corresponda.”
“roundtrip ticket;”
“show a return or onward ticket”
“a ticket to leave New Zealand at the end of your stay.”
“When arriving to our country, return flight ticket and proof of funds during your stay will be required by the inmigration authorities.”
“show proof of a return or onward journey”
“Short-Term travellers should have sufficient cash and proof of onward travel (tickets, visas), and ensure that you do not stay beyond your Visit Pass validity; which is different from Visa validity period.”
“a return or onward ticket”
“Canadian border officials may ask you to show a return or onward ticket and proof that you have sufficient funds to support yourself for the duration of your stay, even if you are staying with family or friends.”
“flight ticket for returning home”
“Entry will not be permitted on a one-way flight ticket, unless the person is in possession of a valid Temporary Work/Study Permit, Permanent Residence Permit or an appropriate visa.”
“show a return or onward ticket”
“Verify that your return ticket is in line with the passport’s expiration date.”
“You may also be asked to show a return ticket or proof of sufficient financial means.”
“Return Air Tickets”
“show a return or onward ticket”
“Return ticket is required for:”
“show a return or onward ticket”
“show a return or onward ticket”
“show a return or onward ticket”
“an onward or return ticket”
“You also need a return ticket or sufficient funds to purchase this.”
“show a return or onward ticket”
“show a return or onward ticket”
“show a return or onward ticket”
“At Cyprus border control, you may also need to: show a return or onward ticket”
“show a return or onward ticket”
“show a return or onward ticket”
“show a return or onward ticket”
“show a return or onward ticket”
“At Polish border control, you may also need to: show a return or onward ticket”
“show a return or onward ticket”
“Border authorities may ask to produce for inspection a tourist travel voucher issued by a travel operator (notarized), a duly certified invitation letter from a natural person or a legal entity, a return flight ticket, a proof of paid hotel booking or a certificate verifying the private residence address during his/her visit, a proof of paid health insurance as well as a health insurance policy for the period of stay in the Republic of Serbia covering possible medical costs that cannot be less than EUR 20,000.”